It was 2am on March 2 and in the following hours, an incident allegedly took place in Mr Hughes' Hataitai home that triggered a complaint to police from an 18-year-old student.
It is understood the complaint - which Labour leader Phil Goff has been aware of for two weeks - is of a sexual nature.
Mr Hughes, at 32 one of Labour's most promising MPs, has denied any wrongdoing.
He is now on leave until the police inquiry is completed.
Mr Hughes, a talented debater, had taken part in the Victoria University Great Debate at the Hunter Lounge in Kelburn, leading the negative team in the moot, "That there should be a universal liquor allowance for students".
National's Tauranga MP Simon Bridges was also debating.
"It's part of the Victoria University Orientation Week, so there was a good crowd, people in good spirits," said Seb Templeton, president of the Victoria University Debating Society.
Mr Hughes, Mr Bridges and about a dozen students went to the Matterhorn bar and restaurant in Cuba St.
"We all had a bit of food, something to drink, and I left about midnight," Mr Bridges said.
"I certainly didn't see anything inappropriate happen."
Mr Templeton said he later met the group again, including Mr Hughes, at The Establishmentin central Wellington.
"There was nothing unusual going on. When I left [Mr Hughes] was just having a chat to people around him, being a good guy. He wasn't particularly drunk... He seemed fine. Most people were in a jolly mood."
Later, the complainant went with Mr Hughes to the home of Labour deputy leader Annette King, where the MP boards.
Police have visited the house and taken some items away.
They have not commented on reports the complainant left the home early that morning and ran into a police car, when he made allegations against Mr Hughes.
Mr Templeton said he was interviewed by the police within a week.
"I wasn't told of any of the allegations. I just gave them a rundown of what happened that night, including what drinks I had at which bars.
"They asked where the complainant was in relation to me when we were in the same place, but they didn't ask me about Darren at all, and at the time I had no idea Darren was involved."
Yesterday morning, police confirmed detectives were investigating a complaint against an MP.
"Inquiries into the matter are continuing but police are not seeking any assistance from the public at this stage," the Wellington district field crime manager, Detective Inspector Mike Johnson, said in a statement.
It is understood the complainant has no formal political connections but has an interest in politics.
A high-achiever at school, he is understood to have been a Youth MP and is now living in Wellington.
Mr Templeton said the complainant was just getting on with life.
"He seems fine. I haven't talked to him about it. I don't think many people have. I can honestly say he hasn't told any of us what the allegations are."
A student, who did not want to be named, said the complainant was keeping up "his usual, confident personality" and had not discussed the incident at all, except with police.
A duty manager at The Establishment, Dushka More, said yesterday that police had not been in contact, and she did not know anything about media reports of officers wanting to look at video footage from the bar.
The Matterhorn also said police had not spoken to staff.
