Before I say goodbye - Mary Higgins Clark

Nell McDermot is devastated when her husband's cabin cruiser blows up. Not only is she shattered by Adam's sudden death, but she is wracked with guilt, because the last time Nell saw Adam alive, she told him to leave and never come back.
Nell's feelings are further complicated by her Great-aunt Gert's insistence that she try to make peace with Adam through a medium. And despite her scepticism, the awful burden of guilt finally drives Nell to consult Bonnie Wilson, a well-known psychic.
As Nell searches for the truth about Adam's death, she relies more and more heavily on Bonnie, who claims to be receiving instructions from Adam. But what Nell does not know is that she is being closely watched, and the nearer she comes to learning what happened to her husband, the nearer she is to becoming the next victim of a ruthless killer…