There are just seven days to go before Mel (Sarah Alexander) and Howard (Ben Miller) get married in the beautiful grounds of her parent's house. As the week begins, the happy couple are blissfully looking forward to their wedding until a panicky call from Mel's mother, Angela (Alison Steadman) disturbs their tranquil morning. Howard has one task to complete before they visit Mel's parents later that evening, but his office friends throw him a surprise drinks party and things don't quite go to plan. And just when Howard was about to put all that behind him, his colleague Cassie (Raquel Cassidy) drops a bombshell, which leaves his entire office disgusted with him. At Mel's parent's house, things go from bad to worse for Howard. Struggling as ever to impress the in-laws, Howard somehow manages to get caught in a compromising position in the toilet, lock the family pet in the grandfather clock, and climb into the wrong bed for a snuggle.

There's an uncomfortable atmosphere during breakfast as Howard faces up to the night before and his accidental bedroom liaison with Angela, Mel's mom. Redemption is at hand for Howard however as the long awaited ring finally arrives. Relations seem to be going well until he receives a petrifying call from Cassie, an ex-flame, who decides to profess her wanton desire for Howard, all while Howard is standing less than two feet away from Mel and her parents. Luckily for Howard, the day is broken up by a visit to Ron (John Benfield), his widowed father, but upon arrival Howard and Mel are welcomed by cries for help. A panicked Howard breaks into his father's home only to receive an embarrassing introduction to Ron's latest girlfriend. Back at Mel's parents, Howard discovers the remnants of a familiar ring-bearing box adorning the gnarled teeth of Binky, the family dog. As Howard contemplates how to extricate himself from this latest situation, an encounter with Mel's Father, Dick (Geoffrey Whitehead), over a wall building project gives rise to an unfortunate mishap involving, Howard, a cement mixer, and poor old Binky.

Mel and Howard return home to find Cassie in a compromising position in their bedroom. In desperation Howard agrees to meet with Cassie to try to put an end to her mad interfering but his plan goes horribly wrong, leaving a distraught Mel searching for her fiancé. Later Howard is determined to put things rights with his future in laws, and brings thoughtful gifts to soften the blow of Binky's demise. Unfortunately the presents get muddled up with a joke gift for the best man and once again Howard is regarded with horror by Dick and Angela. Things turn from bad to worse as Uncle Fraser (Ronald Pickup) arrives for the wedding and the family prepare for Binky's funeral. What more can possibly go wrong for Howard?

Cassie's father turns up at the Cook household and berates Howard for ""abandoning"" his daughter until Uncle Fraser takes charge of the situation and escorts him off the premises. Strained relations between Mel and Howard take a turn for the worse when the wedding program arrives with an embarrassing print error...if only Howard had proof read them correctly! Mel and Howard part for their respective bachelor and bachelorette parties. Mel decides to get drunk and begins reminiscing about past relationships, which leads her to get in touch with an old flame. Meanwhile Howard's evening is one long disaster beginning in the pub and ending in the river Thames.

Howard wakes up in a prison cell to find out some terrible news about his best man Ben. It's a mad rush to the wedding rehearsal but sadly things don't go quite to plan and an ambulance is called to the church. Still they can look forward to a nice meal with the whole Cook family and Howard's father Ron and his lap dancer girlfriend Trish (Lizzie Roper). Howard and Mel are determined not to let their family differences get in the way of their happiness and finally sneak away to enjoy some time to themselves, unfortunately their flirting ends in disaster for Granny Cook (Hazel Douglas).

After the worst week of their lives the wedding day finally arrives, the big question is: are Mel and Howard actually going to make it down the aisle? Granny is in intensive care, Uncle Fraser has an urgent confession and there's a problem with Howard's suit. But the bride and groom remain undeterred. That is, until the father of the bride locks himself in the study and the bride goes missing. Can Howard and Mel make it to the church on time and will Angela's hors d'oeuvres survive until the reception?

Howard's and Mel's lives descend into further chaos. Are they destined to remain unmarried forever? Sunday morning in The Cook household: The father of the bride is nursing a bottle of scotch, the mother of the bride isn't talking to her husband, and their daughter Mel is missing. The police refuse to do anything until she has been missing for 24 hours so it's all up to Howard to try and find his bride. Will they be happily ever after?