Dwarf/professor detective ""Mongo"" Frederickson (An Affair of Sorcerers, City of Whispering Stone) can be an engaging narrator and a disarming sleuth-creation; but here, as in previous outings, the basic Mongo/Chesbro talent is stretched so thin that it's barely visible--in an overlong tale that quickly shifts from murder-mystery to farfetched, comic-bookish sf/fantasy. Mongo goes home to Nebraska for the first time in years--for the funeral of his beloved 14-year-old nephew Tommy. How did Tommy die? Well, according to the police, he and chum Rod (also dead) were homosexual lovers, driven to a suicide death-pact. But Mongo decides to investigate further, suspecting that the local police-chief (a childhood enemy) is under the thumb of the Volsung Corp., an enigmatic company with a big, secretive local plant, involved in genetic engineering. Did Tommy and Rod (science/computer whizzes) somehow stumble onto the Volsung Corp.'s dark secrets? So Mongo believes--especially after there's another murder. . . and after Mongo himself encounters a strange gorilla at the Volsung factory. So, with brother Garth (an NYPD cop) and DIA agent Lippitt, Mongo sets out to expose the horrific genetic doings by the Nazi-ish mad scientists behind Volsung's Valhalla Project; the trail leads to a Wisconsin commune, a super-lab in Pennsylvania; along the way, the Fredericksons are repeatedly captured, tortured, then injected with the Valhalla Project serum. . . which creates reverse evolution! And before the California finale, the Fredericksons will de-evolve (Mongo goes reptile, Garth gets neanderthal), find the antidote to the de-evolution weapon, and begin a doomed friendship with a gorilla-victim of the experimentation. Repetitious mayhem, jokey/stagey dialogue, dollops of heavy sentimentality: a longwinded hybrid that's likely to please a few fantasy readers. . . but nary a mystery-lover.