A Clue in Wax by Fred M. White

Cheriton did not stop to argue the point. "That's your man," he said. "The wealthy gentleman in the car on his way back to the Dormy House after his visit to London on business. The murderer of Lord Seagrane."

For once Merrick forgot his grievance regarding the importation of amateurs and gentlemen inside the sacred precincts of Scotland Yard. He stared at Cheriton with something like admiration in his eyes. But still cynical.