They are opposition members who squeezed into Parliament as Non-Constituency MPs, by way of losing by the slimmest margins at the 2011 General Election.

This year, Mr Gerald Giam and Mr Yee Jenn Jong of the Workers' Party (WP) and Mrs Lina Chiam of the Singapore People's Party (SPP) are lining up again for another shot at endorsement via the ballot box.

This week, Insight looks at the hot spots they contested, which are set to sizzle again.

Mr Giam is returning to East Coast GRC, hoping to better his party's 45.2 per cent result. Then a five-MP constituency, it will become a four-MP one now, with Fengshan carved out as a single seat.

Major infrastructural works there have led MP Lee Yi Shyan to quip that the opposition might need a guided tour for their "once every five years" visit.

Or, will East Coast GRC voters be won over by the WP team, which itself has undergone a facelift? Mr Giam is the only remaining member of the 2011 WP team that was fielded there.

Meanwhile, Marine Parade GRC has absorbed the Joo Chiat single seat, where WP's Mr Yee, casting himself as local-boy-made-good, lost by a mere 388 votes. This, coupled with the fact that the GRC has lost MacPherson, which polled second-highest out of the five wards, means the boundary shifts could well hurt the PAP, which eked out just 56.6 per cent of the votes in 2011.

In Potong Pasir SMC, the PAP won by a wafer-thin 114 votes in 2011, ending a run of 27 years of opposition reign. It had been held by opposition veteran Chiam See Tong.

His wife, Lina, contested it when he went to join the battle for Bishan-Toa Payoh GRC instead. Will Mrs Chiam manage to reverse the result this time round?

And in neighbouring Bishan-Toa Payoh GRC, where the PAP won 56.9 per cent of the vote, a PAP team with three new faces will go up against a joint team from the SPP and Democratic Progressive Party.

Will the national mood, perceived to be less hostile than in 2011, be enough to propel the ruling People's Action Party (PAP) to larger margins of victory?

Or will the opposition make further inroads into Parliament on the back of the unprecedented breakthrough in 2011, when the WP won Aljunied GRC?

Come Polling Day, all eyes will be on these four hot spots, which look primed for a photo finish.