Say this for Willa Jansson (Last Chants, 1996, etc.): She doesn't shrink from the big cases. This time she's down in Santa Cruz, repaying a favor to psychiatrist Fred Hershey by defending his client, mushroom expert Alan Miller, on charges of hit-and- run and vehicular manslaughter after his Fiat landed in a field of brussels sprouts on top of Francis Addenaur's Buick, crushing Addenaur to death. Res ipsa loquitur, says smug ADA Patrick Tober--the thing speaks for itself. Even though Miller wasn't found in the Fiat, it's full of his prints, and no one else's, and he's admitted driving it only an hour or two before the accident. Under hypnosis, though, Miller has given Hershey the wildest alibi imaginable: He was abducted by aliens who dropped the Fiat (which left no tracks through the brussels sprouts) on top of the Buick. When a hitchhiker Miller picked up earlier that evening tells an equally bizarre story about her own close encounter, it's off to the races for Willa, who ends up examining crop circles that may have been made by alien spacecraft, subpoenaing UFOlogists who keep bickering among themselves, keeping Miller away from Addenaur's grieving, well-armed widow, and sweating to protect her real-world job back in San Francisco. All right, the conclusion doesn't live up to Matera's bold, witty challenge to the most rational foundations of the mystery genre, but what could? Willa's sixth still supports her remarkable claim to have ``helped make Santa Cruz a flakier place.''