“Ha ha!” echoed Tuppence approvingly, as she rose.

South Audley Mansions was an imposing-looking block of flats just off Park Lane. No. 20 was on the second floor.

Tommy had by this time the glibness born of practice. He rattled off the formula to the elderly woman, looking more like a housekeeper than a servant, who opened the door to him.

“Christian name?”

“Margaret.”

Tommy spelt it, but the other interrupted him.

“No, g u e .”