I shall always remember 20 December 1931 as the day I made a valuable discovery: if you want to find out more about a person connected with a murder case, the traditional method of asking them questions about all the usual things—their relationship to the victim, for instance, or their whereabouts when the crime was committed—is significantly less effective than this lesser-known method: begin to decorate a Christmas tree in their vicinity

“I shall tell everybody at the same time,” he said. “It is the most efficient way, and the way I prefer to do it. And, Catchpool, you of all people . . . How is it that you need me to give you the answer? As soon as you had spoken to Sergeant Wight on the telephone, you knew all the same facts that I know. You are in the happy position of being able to solve the puzzle yourself.”
I groaned.
“You can, mon ami. All the pieces are now clearly revealed. You need only assemble them in the correct order. Put the little grey cells of Edward Catchpool to work! [...]”