The Unexpected Guest

The Unexpected Guest is a 1958 play by crime writer Agatha Christie.
On a foggy night, Michael Starkwedder enters the home of the Warwicks through a window in the study. He finds the dead body of Richard Warwick, and finds Warwick's wife, Laura, holding a gun that supposedly killed him. Despite the murder being obvious, and overwhelming evidence pointing towards it, Starkwedder does not believe she killed him, and she soon tells him she's innocent.
The two decide to place the blame on an enemy from the past, MacGregor, a man whose son was run over by Richard while he was drunk. As the story progresses, the two fake the fact that they were just finding out about the murder, and others in the house were introduced. It is revealed Laura was having an affair due to Richard's cruel nature, and was vouching for the man she was cheating with when she claimed to have killed Richard. But there are other suspects as well - Warwick's mother, his simple half-brother, the sinister Angell or the apparently goody-goody Miss Bennett. The real murderer could be anyone!