Out of the Past by Patricia Wentworth

James and Carmona Hardwick are spending the summer playing host to numerous friends and relatives in an old Hardwick family residence by the sea. The arrival of Alan Field, a devastatingly handsome though shady figure from Carmona's past, destroys the holiday atmosphere in the old house and replaces it with a mounting tension, culminating in murder. Fortunately, Miss Silver is present to unravel the complex mystery and seek out the murderer amongst them.