Houston, a talented but uneven author of historical novels and thrillers (Bisbee '17, Ararat, etc.), now tries his hand at conventional, if scenic, sleuth-action--with hard-working but soggily derivative results. The series-hero making his debut here is Quintus Paz, a Tucson-based special agent for the US Customs Service--about to leave the Service, at 45, for a security job with his rich brother-in-law. But then Paz is begged to undertake a special mission in Mexico: archaeologist Baron von Hummel has disappeared from Veracruz; his assistant has turned up dead; and von Hummel's exciting new find--a codex that links the Mayans to the to the ancient Hebrews--has vanished. So off goes Paz--first to Mexico City, where he gets beaten up and then discovers the corpse of the fence who was planning to smuggle the codex out of Mexico. Next: on to Veracruz, trailed by assassins. Paz quizzes a corrupt US consul there (murder victim #3). He confronts a few faceless villains, who kidnap the agent's girlfriend Teri (who has joined him for no good reason). And there's a smudge of jungle-mountains action before some final revelations involving drugs (yawn), guns (ditto), and betrayal. Paz remains an earnest, dull stick, despite a contrived tangle of personal stakes: his brother-in-law's a suspect; so's his old Mexican flame; and the Baron was Paz, Sr.'s dearest pal. Every creaky plot-turn is a watered-down clichÃ‰. So, despite some sturdy background atmosphere, this is sparkless journeyman fare--and slow-moving to boot.