Abandoning his series-hero Roger Levin (The Caribbean Account, etc.) and dropping his hip/cute mannerisms, talented suspense-man Furst has produced his best novel yet: a twisty, oblique, ironic tale of the ""private sector"" intelligence business. Guyer, dumped by the CIA in 1977, has gone into the spy business for himself--teaming up with computer-whiz List, a flashy Vietnam-vet and ex-drug-addict, to specialize in providing look-alikes on demand. (Their computer, programmed with thousands of photos from yearbooks and periodicals, can match faces.) And his newest case is a big one: an anonymous client is willing to pay $40,000 for the brief services of someone with a close resemblance to fugitive-terrorist Raoul Delatte. Will the double be in danger? Absolutely not, Guyer is assured by middle-man Benauti. So Guyer & Co. track down a Delatte double--a Wisconsin shoe-salesman--and persuade him (for a $10,000 fee) to cooperate. But, on the weekend of the mission, Guyer's worst fears are soon realized: a man ""identified as Delatte"" dies in a car-crash explosion; Benauti disappears; Guyer, left with the shoe-salesman's death on his conscience, hires a fat manhunt-genius to track Benauti down. . . while disturbing questions arise. Could this disastrous operation have anything to do with Francis Mains--Guyer's old CIA nemesis, now a private-intelligence tycoon who wants to acquire Guyer's outfit? Could there be a leak in Guyer's office: the unstable List. . . or the impassive, super-competent, matronly programmer? And after Benauti is located (with help from that face/photo computer), Guyer puts it all together, quits the business, and opts for retirement with earthy new-love Maggie--but a dandy final twist leaves the way open for Guyer's return to action. Offbeat characters, convincing dirty-trick details, and an intriguing plot that never dazzles but also never exasperates: quirky, grimly atmospheric suspense for the genre's more sophisticated following.