'Padre Island, here we come!' Sandy haired Chuck Merrit scrambled out of the station wagon. . . 'I can't wait to start hunting shells.' Chuck's eight-year-old sister Judy swung her long blond pigtails right and left as she scanned the beach."" Thus, Chuck, his mother, little sister and cousin Roger come to camp on Texas' Padre Island, where Mom, an anthropologist, hopes to find remains of the cannibal Karankawa Indians. What they do find is the shack, complete with parrot, of a hook-handed, gruff but kindly former sailor who calls himself Barnacle Bill. (The parrot keeps asking for ""a little rum,"" but Bill's blue eyes twinkle with pleasure at the offer of root beer, his favorite.) Bill takes them to the site of a Kronk (Karankawa) camp where Mom does pick up some pottery pieces--but who has made the treasure map directing the children to the old wrecked ship where each finds a wrapped present? And who keeps taking hot dogs and brownies and leaving old coins in their place? The answer is not a pygmy or a ghost after all but Bill's unofficially adopted Mexican ""grandson,"" and before the camping trip is over Pepe, Chuck and Roger capture two long-haired, bathless scavengers who threaten to eat Pepe ""Kronk"" style if he doesn't lead them to Bill's supposed treasure. If the opening sentences aren't clue enough to what Silverthorne is dredging up for readers, the chapter headings (""A Midnight Visitor. . . Lost! . . . A Dash for Freedom"") should be.