Michael is testing a new toy, a sausage-firing bazooka. In the process he smashes the living room window. Susan is not pleased. Neither is Nick - the bazooka was integral to his new high speed food delivery venture.
A difficult patient at the surgery inspires Ben to bunk off work and go home early. However the afternoon of relaxation he envisaged is scuppered by Susan who wants him to fix the broken window. Michael meanwhile has retired to his bedroom to do some serious snogging with Fiona.
Roger arrives at the Harper's home in a panic. One of the patients has apparently caught 'Ortes River Fever'. The surgery has been closed and everyone is to adhere to strict quarantine. Ben is furious that Roger has endangered them. Susan however leaps into action. No-one is to leave the house and she will get advice from NHS Direct.
Nick tries to gain access to the house with the pregnant Pamela. But Pamela is just a snake, whose eggs Nick intends to sell. He is refused entry.
Exasperated by his failure to fix the window, Ben finally climbs out of it to escape the quarantine. At the stream in the park he is accosted by a do-gooder, Clarence, who thinks Ben is suicidal. Ben falls into the stream and then goes to Clarence's house to dry off.
Ben is feeling sorry for himself. He says he is a black cloud who makes his family's lives miserable by always complaining. It would have been better for them had he never been born. Clarence says he's wrong and will show him so.
Ben and Clarence magically visit the Harper home. In Ben's place there is another man - Len. He is a chiropodist. Nick is still after money, Susan has just cooked a terrible dinner and Michael is still a know-it-all. Ben joyfully realises the happy truth that without him his family would be just as they are. He has had no effect on their outcome whatsoever - "They're the crazy ones"
Back at the house Susan has finally got some medical advice and apparently there is no such thing as Ortes River Fever. It seems that Roger's patient made the disease up in order to cancel his appointment. Ben returns home ecstatic. He feels something has changed in his life. He grabs Susan for a quick grope in the closet only to find Michael and Fiona have already bagged it.
Beneath the house there is movement - Nick has tunnelled under it so that Pamela can lay her eggs in the warm.
