When his wife, Elizabeth, runs off with Ronald, the Major decides to solve his debt problems by letting the basement flat of his wife's house -- to two different tenants simultaneously! 

Jill, who works in Brussels, only uses the flat at the weekends, while Philip, a barrister, lives there during the week. The Major simply swaps over their belongings at the beginning and end of each week and everything runs smoothly until Jill is unexpectedly given a week off work, just as Philip returns to the flat after his weekend out of town. Further complications arise with the arrival of Elizabeth and Ronald, particularly when Elizabeth lets the flat again.

The Major's resourcefulness is stretched to breaking point but after a wild confusion of mistaken identities, awkward confrontations and hectic misunderstandings, all ends happily for the Major and assorted tenants!