The Stanleys are back from Italy (The Famous Stanley Kidnapping Case), more-or-less resettled in the Westerly House (The Headless Cupid)--where David, a shaky 13, doesn't know what to make of family-fantasizer Blair's nightly jaunts to see a dog in the yard. . . or how to deal with hulking, taunting classmate Pete Garvey. Adolescing stepsister Amanda is an enigma too--admiring Pete's physique, punching him out to protect David, looking sympathetic? pitying? And why does Pete start hanging around? But the problem that grows ever-bigger is Blair's dog. Dad and stepmother Molly quarrel over his clamp-down on Blair's "fantasizing." Six-year-old Blair's twin Esther, and resident-snoop Janie, huddle with him. A neighbor's smokehouse is broken into--only maybe by two escaped cons. On a spooky night--when the cons have just resurfaced, and Dad and Molly are out--the older children discover one thing at least: there is a real dog, a monstrous, gentle Irish wolfhound, whom the little children have named Nightmare. Further sleuthing by Janie (who spotted the breed in a book) explains his old bullet-wound and his fear of grown men: guard-dog training, by a vicious owner. All the more reason, then, to conceal Nightmare from Dad--who's already vetoed the idea of a dog, who'll feel obliged to contact the owner. The ensuing conspiracy is an all-hands, full-time operation. Nightmare spends nights with Blair and David, behind a warily locked door. (Once, Molly does demand admittance.) Days, he disappears--where? Massive as he is, he must be massively fed--hence the kibble caper. Then, for a couple of nights, he doesn't show up; Blair steals off to search for him; David finds both of them--turning up the fugitive cons (sick, dejected), bringing them in, becoming an embarrassed/ pleased hero. Amanda has made her new sisterly feelings known. Pete, confiding his (transparent) interest in Amanda, tells the still-droopy David not to confuse fighting and courage. As for Nightmare, you know Dad won't be able to resist his oversized appeal, his part in the heroics, or Molly's good-natured teasing. ("How could an imaginary dog be a burden?") The family mix continues to work its charm, the personalities to unfold independently--with more to be seen or heard, it appears, of Blair's elusive friend Harriet.