Soporific memoirs of a retired hypnotist-cop who fought a successful uphill battle to make his avocation respectable as a police investigative tool. ""No one really has the answers"" on how hypnosis works, says Diggett; but it often helps witnesses retrieve detailed information lost to the conscious mind--the license plate number of a fleeing car, for example, or an accurate physical description of a suspect. Diggett found hypnosis especially useful in the production of composite drawings, a technique used in the solution of New York's recent ""Phantom of the Opera"" murder case (he hypnotized a Berlin Ballet dancer who saw the victim and the murderer together backstage at the Met). He used a similar approach for help on a composite drawing from a wounded Son of Sam victim (unaccountably, in view of prior publicity, given a pseudonym here). While hypnosis often brings breathtaking breakthroughs, Diggett stresses that it's ""just another tool"" of investigation and that people can, and do, lie under hypnosis (which is why he dismisses as foolish defense attorneys' claims that hypnosis has ""proved"" their clients' innocence). Nor does everyone have the same susceptibility: ""the disposition to hypnosis is a talent . . . and everyone has an in-born capacity to achieve a particular depth."" Though the mechanics involved aren't emphasized, there's plenty of information here on susceptibility testing (can you roll your eyes up and close your eyelids simultaneously?), putting people under, and ""deepening"" techniques. It's all ""natural"" and ""harmless,"" says Diggett, though it can occasionally be dangerous in the hands of ""untrained and irresponsible"" operators. Now in private hypnotic practice (for which part of the book seems an unabashed plug), he helps folks throw off ""the shackles of phobic response""--e.g., alcoholism, smoking, test anxiety, fear of flying. In all: a kernel of interesting material, heavily padded and stiffly written.