Death of a Hussy by M.C. Beaton

A tart with a heart of stone...Maggie Baird is neither kind or generous, but she is very, very rich. So when her car catches fire, with her inside it, there are five likely candidates for the role of murderer. All five had been houseguests at her luxurious Highlands home -- Maggie's timid niece and four former lovers, one of whom Maggie had intended to pick for a husband. All five are utterly broke and all had ample opportunity to tamper with Maggie's car. So finding out who did it will require all of PC Hamish Macbeth's extraordinary common sense and insight into human nature; especially when the killer appears to be the wrong person entirely...