Dylan must contact all the girls he has slept with to inform them he has chlamydia. He casts his mind back to Abigail and a flashback reveals a defining moment he'd tried to forget...
In a flashback to 18 months ago, Luke is enjoying the best sex of his life with psychology student Cleo, but he's keen to avoid deep conversation in case she realises that he's actually quite shallow.
In a flashback to 10 months earlier, Luke drags Dylan and Evie to a posh party in the country. Luke is desperate to sleep with his childhood crush Ilona, who's on his 'things to do before I die' list.
In a flashback to three years earlier, it's Evie's birthday and she plans to tell Dylan about her feelings for him over a quiet dinner, but the evening gets hijacked by their friends.
In a flashback to four years earlier, Dylan panics that he's in a serious relationship with Bethany, while Luke has trouble with his new boss Diana.
Dylan sets about tracking down Phoebe who hasn't returned any of his messages. This prompts a flashback to six years ago when the gang are at a pub quiz.
After confessing his feelings to Evie, Dylan flashes back to an ill-fated weekend in the country with the gang and his hippie girlfriend, Frankie.
Dylan starts seeing Abigail, the hotel clerk from Angus's wedding. Six years earlier, he meets Evie for the first time at a house party.
Angus's friends encourage him to start dating after his divorce. Dylan hears back from Amy and remembers a fling that put him in an awkward position.
Dylan looks at a flat with Abigail, and Luke goes to therapy. Three and a half years ago, Angus and Helen are engaged -- and at each other's throats.
At a whiskey tasting, Evie, Dylan and Luke think back on a drunken awards ceremony, where things didn't quite go as planned for any of them.
Dylan meets up with his old girlfriend Emma. In a flashback, Evie and Dylan feel pressured on Valentine's Day, while Luke woos an ex.
Dylan reconnects with Jonesy, a friend who doesn't recall sleeping with him. Three months earlier, the guys try to cheer him up with a wild night out.
The day after Angus's divorce party, Abigail won't answer Dylan's calls. He, Luke and Evie try to piece together what happened the night before.