"Dial 'M' For Murder" by Jeffrey Hatcher

INDOOR THEATRE
Tony Wendice has
married his wife, Margot, for her money and now plans to
murder her for the same reason. He arranges the perfect
murder. He blackmails a scoundrel he used to know into
strangling her for a fee of one thousand pounds, and
arranges a brilliant alibi for himself. Unfortunately…the
murderer gets murdered and the victim survives.
What happens next is the big mystery!