The Third Alibi (1961)

The Third Alibi
Thriller, Drama
A composer (Laurence Payne) is stuck in a middle-class marriage and finds that his affair with his wife's half-sister (Jane Griffiths) has resulted in a pregnancy. When his wife refuses to give him a divorce he hatches a murder scheme that is too clever by half.
Starring
Laurence Payne, Patricia Dainton, Jane Griffiths, Edward Underdown, John Arnatt, Humphrey Lestocq, Lucy Griffiths, Olive Milbourne, Arthur Hewlett, Annette Kerr
Directed By
Montgomery Tully