Clouds of Witness by Dorothy L Sayers

I think it was the cat. H. M. S. Pinafore

Mr. Parker sat disconsolate in a small appartement in the Rue St. Honoré. It was three o'clock in the afternoon. Paris was full of a subdued but cheerful autumn sunlight, but the room faced north, and was depressing, with its plain, dark furniture and its deserted air. It was a man's room, well appointed after the manner of a discreet club; a room that kept its dead owner's counsel imperturbably. Two large saddlebag chairs in crimson leather stood by the cold hearth. On the mantelpiece was a bronze clock, flanked by two polished German shells, a stone tobacco-jar, and an Oriental brass bowl containing a long-cold pipe. There were several excellent engravings in narrow pearwood frames, and the portrait in oils of a rather florid lady of the period of Charles II. The window-curtains were crimson, and the floor covered with a solid Turkey carpet. Opposite the fireplace stood a tall mahogany bookcase with glass doors, containing a number of English and French classics, a large collection of books on history and international politics, various French novels, a number of works on military and sporting subjects, and a famous French edition of the Decameron with the additional plates. Under the window stood a large bureau.