Married as teenagers Caroline and Liam,now thirty-somethings, have to cope with their own brood's problems - teen-aged Chloe's piercings,Steve's being bullied at school and Mikey's eating food out of bins. Liam's slacker brother Tommy is a useless child minder as the couple work extra shifts to afford a holiday in Santorini and then they have to tell Liam's father Jim that the woman he's dating is a nun. Somehow it looks as if they may end up in a caravan on the rain-swept coast and not Santorini.
It's Caroline's thirty-second birthday and Liam is taking her to see Mamma Mia! on stage. Jim and Tommy have both come to baby-sit but Jim wants to use the kids to lick envelopes for him and Tommy is out of food whilst Liam is obsessed with apologising to Chloe's boyfriend Wayne,whom he attacked with a takeaway after seeing them kissing. With so many setbacks it looks as if the only Mamma Mia! Caroline will be seeing is on a DVD at home.
Liam goes for a vasectomy but,put off by Tommy's horror stories about botched operations,bottles out. Caroline finds out from the hospital and goes with him to make sure he has it done but then starts to have doubts of her own. Jim and Tommy's efforts to teach Mikey morality by returning a toy gun he has stolen to the shop only cause more trouble whilst Chloe falls for Peter, the boy who serves her pizza, because of the romantic way he asks for her order.
Jim is outraged to find that Chloe has a fake I.D. card and accuses Liam of taking it too lightly until it seems that she is using it to go to a rave. Liam and Tommy go after her but end up in a Turkish restaurant with no sign of Chloe and next morning it transpires that she was only visiting a friend. The truly dishonest person however is Tommy,who has to return the signed celebrity photographs he stole from the restaurant.
After the brothers are left a legacy Liam buys a Les Paul guitar,incurring the wrath of Chloe who wanted him to spend the money on her school skiing trip. Tommy loses the envelope containing his cash though Jim is teaching him a lesson and has to learn one himself after trying to steal his best friend's girl. Ultimately Liam must return the guitar. After all the washing machine needs replacing - but at least his love life become legendary after Mikey walks in on his parents' afternoon delight and tells the whole school.
Liam is appalled by the family's dishonesty,Caroline telling a friend Jim is terminally ill so she can go to the hairdresser and not take the kids swimming, Tommy moving in to escape a supposedly crazed girlfriend purely because he is avoiding commitment with a nice ordinary girl and Jim forcing Mikey to sign up for football,rather than dance lessons and cheating in his capacity as referee to give Mikey confidence. But when Jim's chicanery has worked too well and Mikey's confidence has become insufferable it's dance classes for the pair of them.