With eight appearances in the last 12 years, Barnes's PI Carlotta Carlyle has the full-bodied presence of an old friend. Like most fictional detectives, she's fearless and smart-mouthed. Unlike most, she has a social circle, an exercise regimen and an underachieving id (""I never do seem to come close to figuring out this man/woman thing""). She also has an unusually strong affection for her turf, which is Boston, a city portrayed by Barnes as imperiled by rapacious real estate developers. So when home health aide Gwen Taymore asks Carlotta to provide security advice to Valentine Phipps, an old lady struggling to keep her rent-controlled apartment, Carlotta agrees, as much out of civic duty as out of a desire for a paycheck. But Mrs. Phipps's sudden death, which may have been murder, casts suspicion on elusive Gwen, as well as on the building's possibly mob-connected landlord. And when music industry mogul Bronson Hohen hires Carlotta to investigate Mrs. Phipps's family tree, she starts to wonder why her old cronies in Boston Homicide are so intent on barring her from the crime scene. Meanwhile, Carlotta has to cope with assorted domestic crises, such as her adolescent ""Little Sister"" Paolina's homelessness, and her tenant Roz's onslaught of bad boyfriends. The many messy details of Carlotta's life give her character resonance, but they also bog down the rather pedestrian plot, which ends improbably with a twist of multinational intrigue. Still, Carlotta's fans will relish dunking doughnuts again with the genial investigator, a woman who knows a thing or two about urban survival (""Car keys make great brass knuckles""). Author tour. (Sept.) FYI: This is Barnes's first novel with Hyperion, which in September also will reissue Barnes's first Carlotta Carlyle mystery, Trouble of Fools, in mass market.