Cast a Dark Shadow is sometimes referred to as a British film noir. I don't think that's an illuminating description. Really, it's an example of domestic suspense. The screenplay by John Cresswell is based on a play, Murder Mistaken, by Janet Green. Cresswell wrote for film and TV for about twenty years from the start of the 50s and he does quite a good job of disguising the essential staginess of the story. Janet Green was a talented writer, best known for films such as Sapphire and Victim, which dealt with significant social issues.
Cast a Dark Shadow is an unpretentious murder story which has a particularly good plot twist that lifts it a little out of the ordinary. The film was directed by Lewis Gilbert, who would later direct three Bond movies among other things. The cast is above average, with Dirk Bogarde playing an odious young rogue who rejoices in the name 'Teddy' Bare. He is well supported by Margaret Lockwood - a major star whose career was on the rocks at the time this film was released - Kay Walsh, Robert Flemyng, and Kathleen Harrison (playing a housekeeper of quite astonishing, but convenient, stupidity).
Teddy marries a much older woman for money, and then kills her to prevent her making a will which will devise much of her estate to her sister. However, Teddy - who prides himself on his cleverness - is himself rather stupid and his murder actually has an effect very different from the one he intended. Undaunted, he gets to know a wealthy widow (Lockwood, in an uncharacteristic role which she handles with verve) and they get married. But then Teddy becomes interested in yet another woman...
This is an entertaining little movie. The music is by Antony Hopkins who later become a well-known radio presenter; I once attended a talk by him in the mid-70s, an occasion which I remember pretty well. The singer Lita Roza - remembered for 'How Much is that Doggie in the Window?' - appears in the film and sings a song; this contributes nothing to the story, but reflects a gimmick common in movies at that time. One other bit of trivia - the play was novelised in 1953 by Green in collaboration with Leonard 'Arsenal Stadium Mystery' Gribble.