Fatal Encounter by Francis Durbridge
Howard, a well-known book publisher, is concerned for his wife, Joanna. Since returning from the country, she has become unusually distressed, nervous and mysterious. When Howard arrives home to find Perry, a former friend, has been shot by Joanna in a struggle, the story takes a sinister turn. It soon becomes clear that Perry has been blackmailing her and, to protect Joanna, Howard confesses to the shooting and suddenly becomes the centre of a complex investigation where no-one is blameless.