Kem Sokha began the year as a vice-president of Cambodia's biggest opposition party which posed a challenge to long ruling Prime Minister Hun Sen. He assumed the mantle of opposition leader after his exiled predecessor resigned.
Now, as the year draws to a close, much of his political network has been dismantled, and many colleagues are in exile. Holed up in Trapeang Plong prison near the Vietnamese border, he is being questioned for alleged treason.
A 2013 video in which the 64-year-old politician tells members of his Cambodia National Rescue Party (CNRP) that his political strategy had American support has been the basis for the charge. A court in Phnom Penh charged him with "colluding with foreigners" to undermine the country. That led to the Supreme Court dissolving the CNRP and banning 118 of its senior officials from political activities for the next five years. Its seats in Parliament were also redistributed.
Kem Sokha's downfall could not have been more dramatic for someone who helped deliver the biggest political upset to Mr Hun Sen in the last general election. In June, the opposition leader made a public pledge not to seek revenge should his party win next year's polls.
The biochemistry and law degree holder merged his Human Rights Party with the Sam Rainsy Party - named after the now-exiled politician - to form the CNRP before Cambodia's 2013 election.
CNRP became the only opposition party to be represented in Parliament following the polls, capturing 55 of the 123 parliamentary seats. In nationwide local elections in June, the party continued to perform creditably, winning 489 of the 1,646 communes. The ruling Cambodian People's Party won 1,156.
But signs of a political crackdown were then already emerging - with the closure of independent media outlets and an amendment to legislation governing political parties that made it hard for them to associate with anyone who had been convicted. The law came into effect in July this year.
After an overnight raid in September, Kem Sokha was led away from his Phnom Penh home in handcuffs. Mr Hun Sen later cited the 2013 video - reportedly broadcast on YouTube earlier - as proof of Kem Sokha's intention to commit treason.
In a letter drafted by his party using notes from his defence team, the opposition leader said the allegation of treason was "completely slanderous". He insisted that he had tried to win power in a "peaceful and positive" way.
"If the opposition party does not attempt to replace the ruling party, it cannot be called an opposition party," he said in the letter.
Tan Hui Yee