The strength of Hart's latest lies not in its mystery--which is easily deduced--but in its sleuth: 60-something Pulitzer Prize-winning journalist Henrietta O'Dwyer Collins (a.k.a. Henrie O), who, with her modest suits, sensible shoes and disingenuous ways, can charm the truth out of the most venomous foe. Henrie is in San Antonio seeking a friend's granddaughter, Iris Chavez, who has been missing for nearly a week after she suddenly bolted from her job at Tesoros, a gallery renowned for its superior Mexican artwork. The upscale establishment is run by the formidable Garza family, headed by patrician matriarch Maria Elena, but it doesn't take Henrie long to sense that something sinister lies under the family's gracious veneer. With Maria Elena's blessing, Henrie begins to investigate Iris's relationship with the clan, and discovers she can trust Iris's lover, Rick Garza, who, indeed, does produce the missing girl. But what are the two terrified youngsters concealing? After uncovering a conspiracy (and a couple of dead bodies), Henrie finds herself in grave danger. This fifth in the series (after Death in Paradise) is enhanced by Hart's knowledgeable descriptions of fine Central American artwork. In addition, each malicious character is splendid in his small role. And though the plot is slender and the finale melodramatic, Henrie O--sturdy, relentless yet compassionate--carries the show. (Mar.) FYI: Carolyn Hart has won the Agatha, Anthony and Macavity awards. In February, Five Star/Macmillan USA will release Crime on Her Mind ($21.95 272p ISBN 0-7862-1735-9), the first collection of Hart's short stories, many of which also feature Henrie O.