In the tradition of the old Ace Doubles (flip the book over to read the second title), here's the nineteenth Wildside Mystery Double. THE QUEEN OF DIAMONDS: A PSYCHOLOGICAL MYSTERY, by Tracey Landau. Leslie Adams doesn't often get angry, upset, or worried. So when Molly, his sister, first disappeared, Les kept calm and used his head. When he was nearly killed in a house explosion while searching for his sister, well, that rattled him a bit, but still Les kept his wits about him. Now the police are blaming him for the explosion, as well as a botched robbery in which a woman was killed. His schizophrenia is becoming a problem, he's being stalked by a mysterious woman that may or may not exist, and his siblings are questioning his sanity. Understandably, Les is feeling a bit stressed, but he has everything under control. More than that, his delusions are the key to discovering the truth about the robbery and his sister's disappearance. At least, that's what he hopes. The crime debut of a startling new writer THE LUCKY DUCK AFFAIR: A TALE OF MYSTERY, by Mel Gilden. In need of a vacation, private detective Amos True and his companion, Polly St. Jough, accept an invitation to relax aboard Otto Laird's slightly illegal gambling ship, the Lucky Duck. Joining them are movie starlet Clair de Lune, enthusiastic writer Ruth Booth, and a number of other suspicious characters. But True soon learns about Laird's ulterior motive for inviting him and Polly out to sea. The Lucky Duck has become haunted by the ghost of Captain Henry Robbins, a smuggler who years ago commanded the ship. When first one guest and then another is murdered, the ghost of Captain Robbins is the main suspect. Can Amos, with the help of Polly, uncover the real culprit? Another great off-beat mystery by the author of Dangerous Hardboiled Magicians