This is a hard, ruthless, cruel play. David Mamet is a hard, ruthless, cruel writer, a hardline realist, an American Ibsen, and like the grim old grouser, he creates characters who don’t ask for, and seldom deserve, much sympathy. Those who do are collateral damage, victims living in the wrong world at the wrong time. Like most of Ibsen’s plays, Mamet’s can be sickeningly claustrophobic, like a sealed, pressurised chamber, with nobody to remove the bodies.

The scene is a Chicago apartment in 1959. Donny (Kim Cattrall) and her gay friend Del (Douglas Henshall) are waiting for her husband, Robert, to get home: he and their son, John (Joe Ashman), are to take a trip to the woods, and the little boy is fussing over what to take. Del, who feels clearly at home here, seems nervy, fidgeting with his hands and feet, and for a moment you wonder why. The conversation is chatty, intimate, laid-back, though Del likes to utter solemn truths, such as: “A human being cannot conceal himself.” Then a note from Robert is discovered. He’s not coming home. He’s leaving his wife.

Cattrall’s performance is poised, heaving with emotion, but thoughtfully controlled: a masterclass. Donny is a proud, sensual woman, fulfilled and dignified, but more vulnerable and fragile than she thinks. Robert’s betrayal is like a brutal ambush and Donny is the wounded beast, helpless and uncomprehending. And there’s more to come. It centres on a German parachutist’s knife Robert seized in the war — except that he didn’t, he bought it later, in Germany. Why, and when, did he give it to Del? The Cryptogram demands complete attention. A cryptogram is something written in code: you need to decipher it. Look for clues. How long has Robert’s note been lying there? Who brought it? Like some of Mamet’s films (House of Games, Heist), this play is a moral detective thriller, a drama of forensic passion: Mamet is tracking down some crime at the root of human relations. “If we spoke the truth,” says Del, “we could be free.” But he’s wrong. In Mamet’s world the truth is like lies: it brings destruction.