WET WORK by Christopher Buckley (Alfred A . Knopf : $19.95; 265 pp.). When the granddaughter who is the apple of Charlie Becker's eye dies from a drug overdose, it's a safe bet that there's going to be hell to pay. And while an old man's thirst for vengeance normally evokes yawns from neighborhood pushers--and far less than that, certainly, from South American drug czars--Charlie Becker is not your run-of-the-mill outraged citizen. A billionaire tycoon, Charlie not only has the ruthlessness of a corporate raider but, more important, the resources to match the drug lords, million for million. And so the chase is on from New York's Lower East Side to the steamy banks of the Amazon. This is taut, fast-paced action with rich--and frequently very funny--characterizations (three hit men named Bundy, McNamara and Rostow, for instance) and some jungle and Peruvian slum settings that are both scary and nerve jarring.