Mark and Jeremy find themselves in competition for the same woman: Toni from next door. This is not the entire problem with Mark and his love life, rather, he is also lusting after Sophie, a co-worker, but finds himself at a loss with how to put his feelings into action. Jeremy is also pre-occupied, but not with love, with his music.
Jeremy faces a dilemma: money vs. art. Should he put all his time and effort into his music and try to 'make it' or should he be like Mark and get a 9 to 5 job to pay the bills (including three months of rent owed to Mark). Sophie is still the object of Mark's desires and he still fumbles about trying desperately to let her know how he feels.
Mark and Jeremy go to a party to try and find some long lost love, or perhaps someone for the night. At the party Mark meets a cool goth 'teenager' named Valarie, who wants to take their acquaintance to the next level: bowling! This gives Jeremy a chance to hook up with Toni, and allows Mark to take his mind off of Sophie … or will it?
Mark attends a work conference and in the process makes a new friend, Alan Johnson, which upsets the 'El Dude' partnership. This forces Jeremy to consider who could replace Mark as flatmate and best friend. Super Hans is the potential replacement, but he doesn't match up as well. Mark grows a moustache, like his new hero, Johnson whilst Jeremy is haunted by flashbacks to 'the one bad thing' that happened when he was wrecked with Super Hans.
Can you love two people at the same time? Jeremy believes you can, and his gorgeous new American girlfriend puts his taboo bashing beliefs to the test. Mark believes you can only love one person. Besides, he and Sophie, the object of his unrequited love, are getting on really well, especially since he starting hacking into her emails.
Johnson returns, immediately taking a shine to Big Suze, proposing a deal involving her to Jeremy. Mark is caught up in Johnson's "Project Zeus" with his reputation at the workplace hanging in the balance. Geoff makes his first appearance of the season, and Sophie spends some alone time with Jeremy in the hotel room.
In order to avoid spending time with Sophie, Mark gets a gym membership. Whilst there he discovers that Jeremy's ex-wife Nancy is working there. Mark tells Jeremy who then becomes desperate to get back together with her. He decides to take a job as a cleaner at the gym and sets about stopping her from dating Mark's personal trainer Matt.
Jeremy meets his hero, techno musician Russell "The Orgazoid". He ends up working as his handyman, which leads Mark to become suspicious, as it seems that Jeremy's job consists of making smoothies for him. Meanwhile Mark meets Sally at his school reunion, one the few girls who actually ever liked him. It turns out that she has married one of Mark's childhood tormentors, Foz. Mark decides to try and seduce Sally whilst Sophie is away on a business trip.
Jeremy takes Mark on a stag weekend, with a rented canal boat. There, they meet two sisters, Aurora and Lucy, and their father. Jeremy falls in love with Aurora, whilst Lucy becomes sexually attracted to Mark. The father offers Mark a job in India, a way out of his impending marriage to Sophie, whilst Jeremy accidentally kills, and then eats a bit of Aurora's dog.
It's not so long since Mark's new bride Sophie stumbled from the car, looking in appalled fascination at her husband of ten minutes and sobbed, "He's horrible!" As we return for the fifth series of this engagingly filthy comedy, Mark (David Mitchell) is getting drunk and maudlin on wedding champagne as his flatmate Jeremy (Robert Webb) urges him to go out on a double-date: "Beggars can't be choosers, she's an actual woman." Mark - remember, this is a man who once based his romantic strategy on the Siege of Stalingrad - arms himself with a copy of the Friends of the British Museum magazine and goes forth again to search for love.
Jeremy's tortured relationship with his very sweet mother comes under the spotlight. It emerges that Jez has been living off handouts from his mum for years and now he's in line for half of her £40,000 bequest from an aunt. Jeremy's need to self destruct kicks in immediately, as does Mark's inability to stop his excruciating attempts to ingratiate himself with any mature grown-up. He adores Jeremy's mum and hero-worships her Scots Guardsman boyfriend.
Newly promoted Mark decides to enjoy his additional power and wealth by splashing out on a boiler, a 'creamy elephant' sofa and by finding Jeremy a job in the office. Things are also looking promising for Mark in his pursuit of Dobby, the company IT girl. However, a routine fire drill puts his plans into total disarray.
Mark discovers that Jeremy's girlfriend Elena has a guilty secret. But should he tell him when Jez is clearly so happy? In addition to this, Alan Johnson offers Mark the chance to go into business with him. Mark, while reassuring himself that this is his dream offer, begins to see Johnson in a new light. Big Suze inadvertently brings Mark and Jeremy's problems to a head
As a last desperate hurrah before the baby arrives, Mark and Jeremy decide to throw a party. Mark sees it as his final opportunity to reignite his relationship with Dobby, while Jeremy imagines it's a chance to make Elena insanely jealous. But as the evening proceeds, it all becomes a bit of an emotional roller-coaster.
Time is running out for Jeremy as Elena and Gail's marriage is imminent. However, he thinks there may be a way to get Gail off the scene and win Elena back. Meanwhile Mark, although conflicted about becoming a father, is worried that Jeff is becoming a potential rival dad. He decides that he's going to learn to drive so that he can take Sophie to the hospital when the baby arrives. Sophie is delighted, but learning to drive doesn't prove that easy.
Mark and Jeremy are at the hospital awaiting the birth of Mark's baby. Sophie is determined to have a natural birth and doesn't want Mark to transfer any of his anxiety to the baby. Meanwhile, Jeremy is convinced he will never get over losing Elena, until he meets Zahra, whose boyfriend is in a coma.
Jeremy, desperate to avoid living with Superhans, sparks up an old relationship with Mark's siser Sara, and moves in with her and her five-year-old son, Joshy. Mark, meanwhile, in an attempt to deal with a damp patch on his bedroom wall, launches a campaign to be elected chairman of the freehold committee of Apollo House.
As Jeremy's love life takes a surprising turn, Mark deals with his own matters of the heart. A girl he has had a crush on since university is launching her new book, so he seizes the opportunity to see her, telling himself it is endurance, not stalking. He invents a fictitious dinner party to get her into the flat, but things do not look good when she calls to ask if she can bring her husband. In an effort to bolster numbers, Mark gets Jeremy and his friends on board last minute, and by the end of the night the truth about Jez's new romance is revealed to all.
Mark is intent on winning the woman of his dreams, regardless of the fact that she already has a husband, and goes to some extraordinary lengths to do so - including a joint trip to the skin clinic for mole-mapping. On the other hand, Jeremy is determined to get his life on track and not ruin his new relationship. However, trouble seems to follow him around, and when Super Hans asks him to help out a friend, it could spell the end for the El Dude Brothers.