Melancholy derring-do introducing celibate-homosexual Zachary Grayson, a stodgy, middle-aged San Francisco food writer, whose life is turned upside down when he's befriended by the companionable Manny, who suggests he accompany him to Puerto Vallarta. There, Manny disappears, and teenaged scamp and pickpocket-hustler Sal enters Zach's life--as do several life- threatening goons in pursuit of a microchip wanted by various secret agencies of the US government, including the one that employed Manny. Forced into action, Zach is suddenly on the run-- and in love. Desperate SOS calls to his S.F. neighbor, the flamboyantly campy Leslie, lead Zach and Sal into even more hot water, with bullets and poison coming into play before Zach can confide--in his diary--his feelings about men. Tierney, whose Deets Shanahan series (The Iron Glove, etc.) also features an admirably rendered middle-aged sleuth, offers up portraits of homosexuals as deft and multidimensional as those by Hansen and Nava. Purists may quibble that, here, he replaces mystery/detection with MacGuffin-hunting, and now and then dips into bathos, but his writerly skills are also evident.