The Montmartre Murders — Richard Grayson

A painter has vanished: normally an event of no importance, but Théo is the heir to a fortune, and so Inspector Gautier of the Sûreté is put on the case. Then a shady art dealer is murdered. A dealer who had acquired three paintings under dubious circumstances, from a minor artist who died in similarly dubious circumstances.

But why is it that so many people want to gain possession of the paintings now - a princess, a Greek millionaire and even, in a roundabout way, Théo?