Showing Puzzle for Pilgrims by Patrick Quentin

Sally Haven, archelypal rich bitch, dies in mysterious circumstances. No one mourns - but everyone suffers.... In pursuit of his errant wife, Peter Duluth finds himself drawn unwillingly into a nightmarish world of conspiracy, jealous passions and blackmail. Could his own wife be the murderer? Or is she protecting her lover, the dead woman's husband? Marietta, Marlin Haven's unstable sister - would she kill for him too? As pressure and confusion mount, Duluth and the doomed trio travel from Mexico City to Veracruz. Then, another death...and Peter finally uncovers the diabolic sweetness of Sally Haven's revenge.