The Quigleys and the Drysdales are caught in an eternal quadrangle. When Clive and Sonia discover that their respective partners are having an affair, they realize that they are reduced to being the other half of an unpleasant equation. Unwillingly, they join forces in an attempt to save their marriages.

Clive and Sonia join forces as their respective partners continue their clandestine romance. But is Melissa allergic to adultery?

Not only have Vera the cleaner's legs turned blue but Clive's mother is planning to die at ten o'clock.

Who is that following Dave? Why does everybody keep running into Chuck Purvis, private detective?

Dave wants Melissa, but keeps Karen for emergencies.

Clive puts his foot down, gets kissed and likes it. Could there be life after Melissa?

As if Clive doesn't have enough troubles being roped in by Sonia to try to scupper his wife's love affair, enter Lester Whales - the exterminator.

As a result of her affair with Dave, Melissa takes up singing to express her newfound passion - so her husband Clive counters by buying a banjo. While the adulterous couple is being followed by Purvis, the private investigator hired by Sonia, Clive himself is being followed by Lester Whales, the jealous husband of his secretary.

To prevent the tipsy Clive from spilling the beans, Sonia whips him off to a hotel where she finds her problems are only just beginning.

All roads lead to Sonia's country cottage but Dave and Melissa's car breaks down en route, due to a bit of petrol-tank sabotage courtesy of Clive and Sonia. The latter couple do make it to the cottage only to discover another pair making full use of the facilities.

Sonia and Clive are caught by the police lurking with intent in the undergrowth of Sonia's garden. Meanwhile, their respective partners, Melissa and Dave, find that their prospective tryst in a country love nest is well and truly spiked.