The Museum of Desire by Jonathan Kellerman

LAPD Lieutenant Milo Sturgis has solved a lot of murder cases. On many of them–the ones he calls “different”–he taps the brain of brilliant psychologist Dr. Alex Delaware. But neither Alex nor Milo are prepared for what they find on an early morning call to a deserted mansion in Bel Air. This one’s beyond different. This is predation, premeditation, and cruelty on a whole new level.

Four people have been slaughtered and left displayed bizarrely and horrifically in a stretch limousine. Confounding the investigation, none of the victims seems to have any connection to any other, and a variety of methods have been used to dispatch them. As Alex and Milo make their way through blind alleys and mazes baited with misdirection, they encounter a crime so vicious that it stretches the definitions of evil.