The Duke in Darkness is a 1942 play by Patrick Hamilton. A psychological drama set during the French Wars of Religion, it was first staged on 7 September 1942 at the Royal Lyceum Theatre in Edinburgh. It ran for 72 performances (8 October – 5 December 1942) at the St. James Theatre, London, and had a brief run on Broadway in 1944.

Plot

In 1580, during the French Civil Wars, the Duke of Latteraine has been imprisoned in the Chateau Lamorre for 15 years, together with his servant, Gribaud. The Duke has feigned blindness in the hope that it will aid his eventual escape. As the two men play a tense game of chess, it becomes evident that confinement has caused Gribaud to lose his reason. They are visited by an erstwhile friend named Voulain, now in the service of the enemy, who tries to persuade the Duke that he is still loyal to him. Voulain sets out a daring plan of escape. The Duke must decide whether he can be trusted—and determine what to do with a loyal, mad companion who could be the plan's undoing.