Nazi-hunting down in Paraguay, where Helmut Gregor Grigori, Auschwitz' ""Angel of Death,"" lives on utterly unrepentant, understandably paranoid, and apparently unkillable, protected by a troop of bodyguards and by Paraguay's hypocritical head honcho, General Stroessner. Grigori changes identities and abodes with ease and is even continuing his hideous Auschwitz experiments--using the for-sale children of the AchÃ‰ Indian tribe whom he occasionally doctors. Enter Ian Asher, the ""Blue Falcon,"" a renegade Israeli agent of many disguises who has finally tracked Grigori to an Argentine mountain resort (Dr. G. has come partially out of hiding in order to rendezvous with his son). But the assassination plan goes awry, with ghastly deaths for both Asher's lover-accomplice and for a semi-innocent bystander, a New York embezzler on the run who just happens (!) to have been one of Dr. G.'s Auschwitz victims. Yes, Grigori survives again, only to be shattered, however, by his son's hatred--and devastated by Asher's ironic last-page revenge. This stow is based on ""actual episodes in the life of an infamous Nazi camp doctor still living as a fugitive in Paraguay today,"" but it owes many of its plot mechanisms to Goldman's Marathon Man. And Lieberman's naked anger (though the use of Grigori's own self-justifying voice lends some ironic edge) would perhaps have been better channeled into a nonfiction exposÃ‰ Still, like all of Lieberman's work, this is highly professional, leanly composed, and thoroughly readable; and, for some readers, the factual basis will more than make up for the shallowness of the fiction.