Grief Street (1931)

Alvin Merle, a womanizing Broadway matinée idol, is found strangled in his dressing room. The door is locked from the inside and there is no possible other way into the room. Merle is having an affair with his leading lady, while his wife, actress Ethel Wynn, appearing in another play in a theater around the corner, is doing the same with Frank Murray, the stage manager on Merle's play. Newspaper reporter Jim Ryan is investigating the case and meets Jean Royce, a young actress who had been fired from the play while in rehearsals. Everybody, including Michael, the old actor now relegated to being just a stage-doorman, has a motive. The explanation for the murder lies within the script of the play.