When Brian takes up jogging, his wife Hilary is not surprised. She has often told him he should exercise more after all the business lunches he consumes. But when Brian is ostensibly running round the park, he is, in fact, spending a couple of hours with his girlfriend, Wendy, in his good friend George's flat. The arrangement works well for some time, for while Brian is visiting Wendy, helpful George knows that there is no danger of his own dalliance being discovered; for the object of his affection is Brian's wife, Hilary It is all plain sailing until George's wife Jessica returns too soon from a business trip to America and puts the cat among the pigeons.