The Turning of the Tide — Reginald Hill

Emily Salter returned to the sleepy seaside resort of Skinburness where she had spent her childhood holidays to come to terms with the break-up of her marriage to the enigmatic, controlling Sterne Follet. Using her maiden name Emily finally felt free from her husband's presence and the threat that he had calmly issued when she mentioned her plans to leave him.

But Emily's illusion of safety is rapidly shattered as a sequence of sinister events unfolds that culminates in the finding of a body in the water's shallows. It gradually becomes apparent to Emily that whatever is going on she is somehow involved, and so is her husband, but not necessarily on the same side.