Young Dylan is told by a doctor that he has the STI chlamydia and advises him to inform his past girl-friends. Starting alphabetically he chooses Abigail and recalls how he went to a wedding with his friends Evie and Luke. Helen the bride is angry that her groom Angus once dated Evie and wants to get back with her so to help Evie Dylan assures Helen that she is the only one. Dumped by his plus one he befriends the female vicar but ends up bedding the receptionist - Abigail. He must now contact her with his unwelcome news.

Dylan has to go back eighteen months to recall a mature student he had taken a shine to. Anna is the second girl on his list. He meets Abigail for the first time in three years.

In a flashback to 10 months previously, Luke drags Dylan and Evie to a posh party in the countryside at which he is desperate to sleep with childhood crush Ilona McLeod, but he's not the only one with designs on her. Meanwhile, Dylan and Evie amuse themselves by attempting some of the unchecked items on Luke's bucket list with disastrous and unexpected results.

In a flashback to three years earlier, just before Angus and Helen's wedding, it's Evie's birthday, and she's planning to tell Dylan about her feelings for him over a quiet meal. However, before she has a chance, Dylan reveals all of their friends are hiding in the wings to surprise her, including his girlfriend Jane, and Jonno, a horribly incompatible date who Luke has brought along for the birthday girl. An unfortunate sexual mishap then occurs mid-dinner, which results in the gang spending the night in A&E.

In a flashback to four years earlier, Dylan has been seeing Bethany for several months, but when she invites her protective big brother over to dinner a terrifying thought occurs - he has fallen into a serious relationship with her. Meanwhile, Luke drags Evie away from an important photography assignment to go to his work bowling night, hoping to find out why his new boss Diana has turned all the women in the office against him. Back in the present day, Bethany makes Dylan question whether revealing his true feelings to Evie is the right thing to do.

Dylan sets about tracking down Phoebe, who hasn't returned any of his messages, but when he and Luke turn up at her family home, they receive unexpected news. In a flashback to six years earlier the friends are at a pub quiz and Dylan is terrified that Phoebe is pretty much the female version of his best mate. Back in the present, Luke, in a rare reflective mood, pressures Dylan to finally tell Evie he loves her.