Did retired schoolteacher Mary Barton go on a three-day killing spree, murdering and mutilating three young girls and then burying them in her garden in the dead of night? That's the charge that Florida attorney Matthew Hope needs to disprove in this swift but talking and watery legal procedural, tenth in the series (Goldilocks, 1977, etc.). The evidence against Mary is mostly eyewitness, but it seems overwhelming: Several solid citizens claim they saw her with the victims (found when a telephone repairman dug up her garden); a dry-cleaner says that she dropped off a bloodstained dress right after the killings; and her next-door neighbor swears she watched from a window as Mary placed a body in a grave. On the other hand, the Englishwoman paying for Mary's defense--in gratitude for Mary's kindnesses when teaching her--insists that the accused is a saint; and Matt believes that she's innocent. So the lawyer sets out to make his case, mostly by refuting the credibility and reports of the eyewitnesses in courtroom Q&As that eat up the lion's share of the narrative. That's okay, since McBain's dialogue snaps at quark speed and he knows his way around a courtroom--but it's of little impact, because the surprise hook that twists the case around pops up only in two paragraphs before the final pages, when the story careens into Psycho-drama: The entire courtroom development is salted away as red herring. Throughout, shading and bulk are added by extra-case doings, including an affair between Matt and an A.D.A.; background detail on minor, always sharply etched characters (particularly Matt's p.i.-assistants); and musings about Floridian ways. Terrific courtroom patter, but by case's end most readers will declare a mistrial.