A television version of the screenplay by Wilder and Kurnitz, adapted by Marcus, based on Agatha Christie's stage play.

A phlegmatic London barrister defends one Leonard Vole, a "nice, harmless chap" who's on trial for the murder of a widow who had taken a shine to him. The circumstantial evidence against Vole is strong, especially since he's unemployed and stands to inherit a considerable sum from the victim. And to further complicate the defense, the only person who can provide an alibi is Vole's wife Christine, who has agreed to be a witness for the prosecution.