Charlie Muffin, top British Intelligence operative, has just broken up a major Soviet spy network in England. However, a new Director with new ideas takes over and wants Charlie out. But then a high-ranking Soviet spy-master hints that he wants to defect, and both British Intelligence and the CIA want him and will do anything to get him. Charlie may be the only man who can bring the defection off successfully, but is the whole thing an elaborate set-up? And when your so-called allies are stabbing each other and you in the back to get this prize, whom can Charlie trust on either side?

The curtain opens on Domenico Soriano, 50, a wealthy Neapolitan shop-keeper who is raging against Filumena, 48, a former prostitute. They lived together for 26 years as husband and wife and she has cheated him, pretending to be near to death, and convincing him to marry her in extremis. Domenico, however, would rather marry Diana, a young girl, who is already in the house pretending to be a nurse. Filumena reveals the real reason for the marriage to Domenico: she wants to create a family for her three children (Umberto, Michele and Riccardo) who have no idea of who their mother really is.
Domenico is not going to allow this and asks his lawyer, Nocella, to annul the marriage. Filumena speaks to the young men telling them that she is their mother. Filumena accepts the defeat of the annulment, but tells Domenico that one of the three children is actually his. All attempts to find out who his son is fails, and Domenico, after 10 months remarries Filumena accepting to be the father of all three.
In the play Filumena memorably tells Domenico that "Children are children, and they're all equal" (I figli sono figli e sono tutti uguali).