The whole thing was rather amusing, and I propounded the thing as a mock problem to Poirot on the following morning. He seemed interested, and questioned me rather narrowly as to the rents of flats in various localities.

“A curious story,” he said thoughtfully. “Excuse me, Hastings, I must take a short stroll.”

When he returned, about an hour later, his eyes were gleaming with a peculiar excitement. He laid his stick on the table, and brushed the nap of his hat with his usual tender care before he spoke.

“It is as well, mon ami , that we have no affairs of moment on hand. We can devote ourselves wholly to the present investigation.”

“What investigation are you talking about?”

“The remarkable cheapness of your friend’s, Mrs. Robinson’s, new flat.”