Two-thirds of a Ghost

Publisher Tony Kane and his wife host a party in honor of best-selling author Amos Cottle at their Connecticut home. But all eyes are on the guests when an unseen hand slips cyanide into Cottle's drink.
Also present at the party is Basil Willing, a psychiatrist-sleuth who soon figures out that Cottle was not the man that his jacket-flap blurb said he was. Willing embarks on a course of literary detection, scouting for clues in book reviews, publisher correspondence, and other documents related to this rather ghostly writer ...
Helen McCloy, born as Helen Worrell Clarkson McCloy (she also published as Helen Clarkson), was an American mystery writer, whose series character Dr. Basil Willing debuted in Dance of Death (1938). Willing believes that "every criminal leaves psychic fingerprints, and he can't wear gloves to hide them." He appeared in 13 of McCloy's novels and in several of her short stories. McCloy often used the theme of doppelganger, but in the end of the story she showed a psychological or realistic explanation for the seemingly supernatural events.