It's mum and dad's anniversary, and the boys come home to hear them giggling upstairs in their bedroom. To their dismay, dad emerges in just a pair of green underpants, and promptly tells them, "Your mother and I were just making love". Revolted, the boys go and sit in the car for twenty minutes until dad comes out to announce: "All done".

As a surprise anniversary present, dad has painted a portrait of mum. It's absolutely terrible and bears no likeness to her at all. In fact it looks more like Margaret Thatcher. Mum is horrified. Dad promptly hangs it up in the downstairs landing for all to see. To make matters worse, Jonny has just had a tattoo done of a skull on his arm, with the words "Live fast die young" in Latin. Mum's anniversary evening is getting worse and worse.

But when Jim turns up heavily sedated, having accidentally swallowed his dog's sleeping pills, and falls asleep on the stairs, the evening goes from worse to terrible. Soon, Jim starts sleep-walking, causing chaos all around the house, before locking the family in dad's study. How will they escape? And can grandma save them?