A delightful comedy of manners starring Oxford professor and amateur sleuth Hilary Tamar, the last in a series of four. In this installment, the story veers from Britain to Cannes, Avignon, and Monte Carlo. The action (as usual) involves taxes and a group of trouble-prone attractive young barristers. It's all very droll, much better than it might sound in a plot summary.  (FRN539, $7.99)