Someone at the Window is a stage play by Agatha Christie which was never published nor performed. It is reworked and expanded from the story The Dead Harlequin. In the play, expands on the plot in the original short story but Christie removed the characters of Harley Quin and Mr Satterthwaite. Julius Green postulates this might have been because the character of Harley Quin is difficult to portray on stage. When this play was written is uncertain. The play includes a two-act flashback section to 1919 at "Canforth Castle" and in the third act the scene shifts to London in 1934. Thus a reasonable estimate is that the play was written in 1934. The play script is long, being some 175 pages and includes a cast of 16 characters, far larger than in the original short story. This and other production difficulties may explain why it was never performed. This play has a number of other features: it is the first to experiment with the theme of time and memory. It also features a murder during a fancy dress ball (like in The Affair at the Victory Ball).
- Julius Green, Agatha Christie: A Life in Theatre, (London: HarperCollins, 2018), 129-135, ebook edition. Green mentions that he consulted two copies of the script which are in the Agatha Christie Archive maintained by the Christie Archive Trust.