An alleged extramarital affair causes the incumbent MP to step down. His sudden departure pits a minority candidate from the ruling party with a deep grassroots background against a veteran opposition figure with a confrontational past but also a reputation for championing civil liberties.
The Bukit Batok by-election was certainly not lacking in compelling narratives. What does the result say about the issue of race in Singapore politics? Is Dr Chee Soon Juan's political comeback on track? How much does estate upgrading matter as an election issue?
And is the "by-election effect" still relevant today?
Insight takes a look at what lessons can be gleaned from the May 7 Bukit Batok by-election.
1. Bye bye, by-election effect?
The much-trumpeted "by-election" effect failed to work its magic for the opposition this time round.
After losing two previous by-elections, the People's Action Party (PAP) won Bukit Batok with 61.2 per cent of the vote on May 7.
Observers believe that in a by-election, voters are more willing to support the opposition as there is no danger of inadvertently voting the Government out of power.
So why did the by-election effect not propel the Singapore Democratic Party (SDP) to victory?
First, for all its purported potency, it is not easy to pinpoint specific instances of the by-election effect at work.
In the first 15 years of independence, the PAP handily won all 11 by-elections that were contested in a bygone era when the ruling party held every single seat in Parliament.
Then came the seminal 1981 Anson by-election, which saw the PAP vote share plummet from 84.1 per cent to 47.1 per cent within a year - a 37 percentage point swing.
While this is a seemingly powerful example of the by-election effect, the PAP's analysis identified a unique local issue that was a key reason for the defeat.
A large chunk of the voters might have expressed their dissatisfaction at the ballot box as they were going to be resettled and were not given priority in getting new Housing Board flats.
Since Anson, there have been four by-elections, and the Workers' Party (WP) has won two of them.
But those two victories also do not conclusively prove this by-election phenomenon.
The 2012 Hougang by-election was contested in the WP stronghold, which it had been holding since 1991. It came as no surprise that it easily retained the seat. In the 2013 Punggol East by-election, the WP won a much closer fight.
But there were also unresolved local issues such as uncompleted upgrading works at Rivervale Plaza and a lack of coffee shops in the new estate.
The PAP's candidate was a new face that was unfamiliar, while the WP candidate had a degree of recognition, having contested there in the previous general election.
To find the most convincing instance of the by-election effect, one has to ironically look at the 1991 General Election.
Opposition MP Chiam See Tong devised a strategy to contest fewer than half the parliamentary seats so that the PAP was returned to power immediately on Nomination Day. With the guarantee of a PAP Government, voters were thus free to vote for the opposition, he argued.
Fighting a general election as a by-election would achieve what he termed a "by-election effect", a turn of phrase that endures in Singapore politics till today.
The strategy is widely credited with delivering four elected parliamentary seats to the opposition, a record that stood until 2011.
But is the by-election effect still relevant in today's political climate, where voters have shown an increasing desire for diversity in Parliament and more alternative voices?
After all, the biggest opposition breakthrough to date - the WP's win in Aljunied GRC, the first time the opposition won a GRC - was achieved in the 2011 General Election when all but one constituency were contested.
The opposition has also not pursued the by-election strategy in the last three general elections, contesting more than half the seats in 2006, 2011 and 2015.
Last year's elections even saw all constituencies challenged for the first time since independence.
The result of the Bukit Batok by-election seems to confirm the receding influence of the by-election effect. Undoubtedly, some voters felt unencumbered to vote for SDP's Dr Chee Soon Juan because they were merely choosing an MP and not determining the government of the day.
But perhaps Bukit Batok merely confirms what past results have suggested: The by-election effect does not exist in isolation, as other factors such as local issues and the quality and familiarity of the candidate play a crucial role too.
2. A boost or a blow for SDP?
What lessons the Singapore Democratic Party (SDP) draws from the Bukit Batok by-election will depend on how it views the result.
The party feels it gave the polls its best shot, having walked the ground daily for almost two months from the time it was clear a by-election would be called.
Those efforts translated into 38.8 per cent of the vote for its candidate and party chief Chee Soon Juan.
In the polls' aftermath, two schools of thought have emerged, each with opposing views about whether this is a good result and what it says about the political future of Dr Chee.
The first camp believes that his performance bodes well for his next electoral contest. After all, this is his best score in five bids for a parliamentary seat since he entered politics more than two decades ago.
The result was an 11.8 percentage point erosion of the People's Action Party's (PAP) 73 per cent vote share in Bukit Batok in last year's general election. In the 2013 Punggol East by-election, which was won by the opposition, the PAP's support fell by a slightly lower 10.8 percentage points.
It was also an improvement on Dr Chee's 33.4 per cent when he contested Holland-Bukit Timah GRC in GE2015, his first since he began putting his formerly more confrontational style of politics behind him.
As such, his more moderate image now is seen as winning increasing support and would give the party good reason to stay the course.
Others, however, are not so sanguine about Dr Chee's electoral prospects.
In this group are several opposition politicians who believe that the circumstances of this by-election were as good as they could get for the SDP leader to be elected.
The PAP's image had been bruised by the scandal surrounding the previous MP, Mr David Ong, who stepped down over an alleged extramarital affair.
Also in Dr Chee's favour were the proverbial "by-election effect" and the small size of the single-member constituency. So a candidate did not have to cover a great area to reach out to voters.
Given the various factors in his favour, they think Dr Chee underperformed, and blew his best chance yet at entering the House.
Reform Party chief Kenneth Jeyaretnam contradicted Dr Chee's view that the media was biased against him and said coverage of the by-election was "fairly balanced and much more equal time has been given to reporting the SDP's rallies and press conferences".
In a series of online posts, veteran opposition politician Goh Meng Seng dissected Dr Chee's result.
In his view, while Dr Chee managed a seemingly impressive vote swing of more than 10 percentage points, that showing is not as good as it looks.
To go from 26.4 per cent, which is the SDP's Bukit Batok result last year, to 38.8 per cent now is relatively easy because voters in that range are more easily persuaded to back the opposition, argued Mr Goh, who heads the People's Power Party.
Anything above 40 per cent requires winning over a bloc of increasingly politically neutral voters.
Get closer to 50 per cent, and one encounters greater resistance from voters who naturally lean towards the PAP, he added.
But the SDP has never crossed the 40 per cent mark in five general elections with Dr Chee at the helm, Mr Goh pointed out.
"He is just unelectable. This is the cruel but honest view I have with regard to Chee," he concluded.
Is Dr Chee the man who can guide the SDP in winning over that crucial 10 per cent of voters to put them over the top?
Those who do not think so point to a factor weighing on Dr Chee: his falling out with his one-time mentor, former opposition MP Chiam See Tong. Mr Chiam left the SDP after infighting within the party shortly after Dr Chee joined its ranks.
During the Bukit Batok campaign, his wife, Mrs Lina Chiam, spoke up twice against Dr Chee and pointedly stated that Mr Chiam did not endorse any candidate in the by-election. In a political landscape where the opposition usually makes a showing of unity, it was possibly more potent than any attack on his character the PAP could muster.
For now, party members are opting to keep the faith in the SDP leader. Last week, SDP chairman Wong Souk Yee issued a statement denouncing negative comments made in a news report about Dr Chee's political career.
Under Dr Chee, the party retains a niche appeal among those most concerned about civil liberties, as the Workers' Party is relatively less vocal on the intangible issues such as freedom of speech.
Still, the question of leadership succession lies ahead. Dr Chee is 53 and will be in his 60s after two more general elections.
No other SDP member has the same high public profile, and the party will have to groom a new generation of leaders within the next 10 years.
To Dr Chee's supporters, it will be a daunting task to fill the personality void when he steps aside.
To his detractors, Dr Chee's relinquishing of the reins of leadership is the first step the SDP must take on a route towards a brighter political future.
3. PAP's winning strategy
The People's Action Party (PAP) pulled off a winner with Bukit Batok, not just in holding the seat, but also in election strategy.
The PAP showed that it had learnt from its poor performance in 2013's Punggol East by-election, when it fielded political newcomer Koh Poh Koon. The colorectal surgeon was widely seen as having been parachuted in, and lost to the Workers' Party's Ms Lee Li Lian.
That the party had re-strategised this aspect was seen in its landslide general election victory last September, when by the time it was called, most of its candidates had been working the ground months - if not years - ahead.
Step forward its Bukit Batok by-election candidate, Mr Murali Pillai. A candidate who:
Had long worked the ground there? Tick.
Mr Leow Boon Swee, who succeeded Mr Murali as branch secretary, said the latter had the know-how and relationships to ensure services for residents would continue.
Is capable of a more personal campaign? Tick.
Is comfortable with party big guns lending their clout? Tick.
But why did this strategy prove successful - Mr Murali garnered 61.2 per cent of the vote - in a by-election some thought would be a closer fight? After all, his rival, the Singapore Democratic Party's Dr Chee Soon Juan, had re-strategised, too, showing a more relaxed side to the war horse of years past.
Also, Mr Murali was a minority race candidate, with history against him (see separate story).
THE PERSONAL TOUCH
First, by fielding someone with a long track record in Bukit Batok, the PAP was assuring residents that it would live up to its promise of uninterrupted projects and services.
Not only had Mr Murali spent the past four years in Paya Lebar ward in Aljunied GRC - where he lost narrowly - but also Bukit Batok was where he earned his grassroots wings. He started volunteering in 2000 before becoming PAP branch secretary in 2007.
Mr Leow Boon Swee, who succeeded Mr Murali as branch secretary, said the latter had the know-how and relationships to ensure services for residents would continue.
While another party could set up another town council and vow to keep services like free legal clinics running - as the SDP's Dr Chee assured residents he would - Mr Leow said it was not that straightforward.
"There could be an impact on the volunteers, not just the party activists. If the results were not good, they may be demoralised, some of them might quit and this could affect the services," he said.
Second, Mr Murali opted for a more personal approach during the campaign.
He held only two rallies - half the number held by Dr Chee - preferring to spend his nights away from the media glare, making the exhausting rounds of visits to residents' homes.
Away from the media glare, he talked to them at length about his proposals including a job placement programme and a health cooperative, promised to follow up on complaints and listened to suggestions on national policies.
Former Cabinet minister Lim Boon Heng, who mentored Mr Murali in the Aljunied GRC team, estimated the candidate might have covered only 20 per cent of the flats in a block each time, but his interactions were "unhurried, engaged, and if some of them wanted to talk to him, he would spend the time".
BIG GUNS TAKE AIM
Another key strategic aspect of the campaign's success was in not just bringing in PAP heavyweights to lend their weight, but in giving them the role of taking aim at the opposition where necessary. Moreover, Mr Murali was a candidate who could handle this strategy, staying above the fray while the big guns fired.
By doing this, he sent a clear message: He would focus on how he could best serve residents.
Mr Murali would not be drawn into commenting on Dr Chee, even after PAP big names like Prime Minister Lee Hsien Loong criticised the SDP chief's character and ability to be an MP.
So were there any downsides to the PAP's Bukit Batok strategy?
While some observers say it is the PAP's prerogative to tap its natural advantage, others say its extensive resources - especially in human capital - steamroll the opposition in terms of resident contact.
Mr Murali saved precious minutes by having at his disposal activists who could run ahead to knock on doors, to find who was home.
The move to let Mr Murali focus on resident concerns, while others in the party took the role of criticising his opponent, may also leave some wondering if he will live up to his promise to be a notable presence in Parliament.
But for the moment, buoyed by a skilful campaign, he gets the opportunity to do so.
4. The race factor now diluted?
News in March that the People's Action Party (PAP) would field an Indian candidate in Mr Murali Pillai momentarily set the coffee shops abuzz in normally sleepy Bukit Batok.
Coming a day after the Singapore Democratic Party (SDP) announced party chief Chee Soon Juan as its candidate, many voters wondered: What is the PAP thinking?
After all, Bukit Batok has known only Chinese MPs since the seat was formed in 1972. Party activists felt that former MP David Ong had a slight edge in votes in GE2015 because he had faced the SDP's Mr Sadasivam Veriyah, an Indian candidate. Now, not only was that edge erased, but also Mr Murali faced the same issue. And yet, the by-election resulted in a convincing 61.2 per cent vote share for Mr Murali.
So is a candidate's race less significant to voters now than in the past?
A FACTOR IN THE CAMPAIGN
To some long-time residents of Bukit Batok, the prospect that their MP could be non-Chinese was disconcerting. One resident who wanted to be known only as Mr Koh, 86, felt that fielding a minority-race candidate would inevitably lose the PAP some votes, even though it had done a good job maintaining the estate. "The majority of us in Bukit Batok are Chinese, so of course it will influence some decisions," he said.
Even as the PAP sought to downplay the race factor, the campaigns showed both parties were attuned to its importance.
Mr Murali, who contested last year's general election in Aljunied GRC as K. Muralidharan Pillai, introduced himself as Murali Pillai this time, and as "Ah Mu" to residents.
A similar campaign to show that language - and, implicitly, race too - would be no barrier between Mr Murali and Bukit Batok residents was seen on social media.
One of Mr Murali's most popular online postings was a video of him speaking Mandarin to residents and introducing himself in Mandarin to the camera. At the same time, a video clip of Dr Chee singing the Hokkien classic "Ji Pa Ban" (one million dollars) made its rounds, as did two video testimonials where Chinese intellectuals expressed support for him.
In essence, race was very much a "silent presence" during the race, said National University of Singapore (NUS) sociologist Tan Ern Ser. "It's silent because it cannot be openly used to garner support, and present, because it cannot be ignored."
Former NMP Zulkifli Baharudin noted that Dr Chee made the effort to speak in Hokkien and Mandarin at his rallies. "It's not just about race but also about language, and Dr Chee wanted to show that he can make a connection with the heartland Chinese resident," he said.
Singapore Management University law don Eugene Tan agreed: "Both candidates recognised that ethnic Chinese voters are the dominant group. You could see that they tried to reach out, tried to persuade voters that they could be counted on to understand their concerns."
BUT AT THE BALLOT BOX...
As it turned out, voters handed Mr Murali one-and-and-half-times the number of votes they gave Dr Chee, a victory wide enough to nullify the comparatively small effect of race.
NUS' Dr Tan said while race may matter, it was very much eclipsed by other factors such as each party's brand and track record.
Analysts also said Mr Murali had prevailed because of other factors such as his likeability, his professional reputation as a high-flying lawyer, and his record of having served Bukit Batok for 16 years.
"The fact that the minority candidate won convincingly in a constituency where the racial profile mirrors Singapore society is actually a tremendous testimony to Singaporean voters' discernment and ability to assess a candidate more on merit than on his skin colour," said SMU's Associate Professor Tan.
This is not to say that race, as a factor, no longer matters. Some of Mr Murali's critics online charged that he had "sinicised" himself to win. Pointing to the Mandarin clips and how he simplified his name, they said "Ah Mu" made himself seem more Chinese to boost his appeal to Chinese voters.
But analysts disagreed, noting the distinction between broadening a candidate's appeal and playing the race card.
An SMC contest also differs from a GRC one, where multiracialism is self-evident in a diverse slate.
"The key message both candidates wanted to get across was that they would be the best person to represent residents' interest in Parliament," said Mr Zulkifli.
GRCs STILL RELEVANT?
Some quarters, like former Singapore People's Party (SPP) candidate Ravi Philemon, argue that Mr Murali's decisive victory refutes the idea that GRCs are needed to ensure adequate minority representation.
Former presidential candidate Tan Cheng Bock noted GRCs were put in place to address concerns that minorities may not be represented, and said: "This victory by Murali has put paid to this fear and should pave the way for the removal of any race-based politics in future."
However, others argue that the way Mr Murali's campaign was run in fact showed the continued necessity of GRCs. Said NUS' Dr Tan: "The GRC system, in principle, is consistent with our multiracial society. It prevents race from becoming a factor."
Most analysts are, however, confident that Mr Murali's win does represent a broader trend.
"You can't conclude that we are completely colour-blind, but this election was clearly not a test of a Chinese candidate versus an Indian candidate," said Mr Zulkifli.
"It shows that multiracialism is a value that has become a deep part of our lives, something that we have accepted and ingrained."
5. 'Ground game' evolving
During the Bukit Batok by-election campaign, when the People's Action Party (PAP) candidate Murali Pillai said he would implement a $1.9 million infrastructure plan should he win, some were quick to point out that his upgrading promise seemed conditional.
Mr Murali's rival, Singapore Democratic Party chief Chee Soon Juan, said it was similar to the PAP's strategy in the past of using lift upgrading to win votes.
Opposition MPs weighed in, too. Non-Constituency MP Leon Perera of the Workers' Party said in a Facebook post that Mr Murali's announcement "recalls the painful memory of the votes for HDB upgrading message in the 1997 General Election", and questioned if such a campaign message was necessary.
But Mr Murali was quick to distance himself from the carrot-and-stick approach, explaining to the media that the Neighbourhood Renewal Programme he had talked about was "funding-neutral". This meant the funds would be disbursed to whichever MP was running the town council, and were not dependent on the PAP winning the by-election.
It indicated that the tactic the PAP had unabashedly used up till the mid-2000s to woo voters - by dangling upgrading goodies and delivering them only if the PAP MP was elected - would no longer work now, some analysts say.
ADVANTAGE AS THE INCUMBENT
It is a matter of fact that when you have a PAP Government, the PAP town councils are better placed to acquire grants from the Government, although of course there are other criteria. But that is the advantage of being the incumbent.
FORMER NOMINATED MP ZULKIFLI BAHARUDIN, who managed two town councils in the 1990s.
Former Nominated MP Zulkifli Baharudin, who managed two town councils in the 1990s, says: "It is a matter of fact that when you have a PAP Government, the PAP town councils are better placed to acquire grants from the Government, although of course there are other criteria. But that is the advantage of being the incumbent."
But the PAP Government knows it has to be fair to all constituencies, including opposition-held ones, as the electorate matures.
"Increasingly, voters want to see more fair play in our political contests and will scrutinise more closely the PAP's value of fairness," he adds.
Singapore Management University (SMU) law academic Eugene Tan says the ruling party's upgrading message would likely hurt its campaign if done in an opposition-held constituency.
But the message had no significant impact in Bukit Batok as the seat had been under the PAP since it came into existence in 1972. "Residents have come to expect value and continuity from the PAP, and upgrading is an integral part of its track record and value creation," he says.
Indeed, pavilions, parks, fitness corners and covered walkways linking several blocks are a common sight in the constituency. All eligible blocks have had their lifts upgraded to stop on every level.
Residents' gripes about the estate were mainly minor, or unwarranted in some cases. Take housewife Kylie Wu, 51, who had said: "I hope they will build enough covered linkways such that, on a rainy day, I don't need to use an umbrella when I go out."
But as it is, there is a sheltered walkway near her block leading to a coffee shop and stores two blocks away. If Madam Wu wants to get to the market and the bus stop, she need only open her brolly once to cross a road.
Dr Gillian Koh, deputy director of research at the Institute of Policy Studies, says upgrading, estate renewal plans and town council management come under the issue of liveability, though some residents may also view estate issues as having an impact on the value of their housing assets.
She explains: "In the HDB heartland, especially a place like Bukit Batok, the 'liveability' issue is very much affected by the quality of the town council and what the state can offer to improve the estate.
"This is different from constituencies with more condominiums and private housing estates."
She adds that both by-election candidates had identified estate management as a key issue as they sought to convince voters of their value to the estate. Dr Chee had tried to assure residents the SDP was prepared to take over the town council from the PAP, and was confident of running it well. Even before the Writ of Election was issued, the party had put together a four-man team ready to help with transition issues should he win.
But Mr Murali, with the incumbency advantage of having grassroots leaders who were strong on the ground and knew what enhancements were wanted, had announced fresh neighbourhood renewal plans, says Dr Koh.
When the upgrading tussle erupted, "the PAP team clarified that... these were plans it had come up with and any other party can come up with its own plans and go through the same process (of implementing them)", says Dr Koh.
Still, SMU's Associate Professor Tan points out that highlighting town council management is strategic. "It (the PAP) has been emphasising to residents that it is a party that can be trusted: It promises and delivers," he says. "It is indirectly reminding voters that the opposition party can promise the sky, but can it deliver?"
For now, the SDP needs to gain trust on the ground, says Dr Koh, adding:"The ground game matters. Politics is local and if you can grab enough trust and credibility, voters give you the mandate to speak at the national level in Parliament."
As 42-year-old Bukit Batok resident Christopher Tong puts it: "Everything in this estate has been going well so far. The area is clean and any issues are resolved quickly. So I don't see a need to change anything at all."