Allan Harding, a teacher in early middle age at a bog standard comprehensive, married to his boring dogooding wife Belinda , is seduced with his full cooperation by a younger colleague Jo. When Belinda, who has all the money, inevitably finds out, Allan is faced with a choice. He can either give up Jo, with whom he has become besotted, and stay with his wife. Or he can leave his wife and his job and the money and take up with Jo. Jo, who really only wants the money, resolves his dilemma by insisting that he kill Belinda during a holiday in Scotland by fiddling with her insulin (she is diabetic). They will dispose of the body in a loch, then Jo will impersonate Belinda for the duration of the holiday to confuse any investigation. When in Scotland he is faced with killing Belinda he chickens out, and Jo has to do the deed. This sours the relationship, and henceforth they are bound together only by their guilt and greed.At the end of the holiday, Jo, travelling south separately, is killed in a rail crash, and Allan is forced to identify her as Belinda. The police in Allan"s patch investigate Jo"s disappearance but officially draw a blank. Sandy, a young DC, smells a rat and travels to Scotland to find out the truth. She finds Belinda"s body in the loch. Allan has gone north to retrieve Jo"s car, which they have been forced to leave in a remote spot in the hills. Sandy finds the local police gathered around the car. She tells them her story and triggers off a helicopter chase which results in Allan"s falling to his death over a bridge. The police conclude that Allan, if he"d played his cards right, could have got away with it and kept Belinda"s money.