The Bolds rescue an endangered victim of anti-fox bias; turns out, there's a downside.Someone's stealing food from the anthropomorphic hyenas' cheerfully chaotic household. Suspicion falls first on family, then their students learning to pass for human: Craig, the wild boar and aspiring (nonalcoholic) craft-brewery entrepreneur; Paulina, the otter with a religious vocation; and Snappy, the goose and likely future traffic cop. The scent of fox reveals the culprit. Human neighbors, also victims, call a meeting and, opposed only by the Bolds, vote to hire a catch-and-release service to remove the fox (extermination's the true plan). Concern for their fellow wildlife leads the Bolds to concoct a daring rescue, but the human-hating fox thief, Mossy, (both his grannies were killed in fox hunts) rejects their help. Sylvie, Mossy's meek vixen companion, can't change his mind. The Bolds are "a disgrace to their own kind," Mossy sneers. Then disaster strikes. Rescued but ungrateful, Mossy's the houseguest from hell, ruthlessly bullying his kindly hosts. With Clary sounding heavy themes (bias, bullying, animals and humans behaving badly), Roberts' unparalleled illustrations, crafting endearing eccentrics from a seamless blend of human and animal traits, add needed buoyancy. Devout Paulina, menacing Mossy, and indignant Snappy are standouts, like the hyenas, again collapsing in hysterics over Mr. Bold's appalling jokes.The unusually weighty plot occasionally clashes with the familiar outrageous puns and potty humor, but series fans will be more than satisfied. (Animal fantasy. 7-10)