A Can of Worms — James Hadley Chase

Private detective Bart Anderson is hired by Russ Hamel, a millionaire author, to shadow his beautiful wife, Nancy. For Hamel has been receiving poison pen letters claiming that his wife has been having an affair. But as Bart's investigation progresses, he discovers that he has opened up a can of worms - for Nancy is not the faithful wife her husband assumes ... 'The thriller maestro of the generation' Manchester Evening News