Witness for the Prosecution follows the case of Leonard Vole who was accused of murdering Emily French, a 56-year old maiden lady who had taken a liking to the young Mr. Vole. Vole is defended by the solicitor Sir Winfred Robards and his main hope to clear his name is the testimony of his wife, Romaine, a foreigner from Germany.
The play has a large number of roles with the larger ones being:
Sir Winfred Robards - solicitor
Leonard Vole - defendant, about 27
Romaine - wife of Vole
Myers - prosecuting attorney
Justice Wainwright - judge
Janet MacKenzie - housekeeper for Emily French
Mayhew - solicitor
Greta - Sir Winfred's typist
Hearne - detective inspector
with many additional roles for men and women as jurors, witnesses, and others.