Maigret takes on a complex undercover investigation in the heart of Paris

What he thought he had discovered, in place of the joyful candour that she usually displayed, was an irony which was neither less cheerful nor less childish, but which troubled him … He wondered now if his exultation wasn’t down to the fact that she was playing a part, not just to deceive him, not just to hide something from him, but for the pleasure of acting a part.