He fumbled for his hat.  With nervous, trembling fingers he held it deferentially in his hand whilst he rose from the table.  Polly watched him as he strode up to the desk, and paid twopence for his glass of milk and his bun.  Soon he disappeared through the shop, whilst she still found herself hopelessly bewildered, with a number of snap-shot photographs before her, still staring at a long piece of string, smothered from end to end in a series of knots, as bewildering, as irritating, as puzzling as the man who had lately sat in the corner.

CHAPTER IV

THE ROBBERY IN PHILLIMORE TERRACE

Whether Miss Polly Burton really did expect to see the man in the corner that Saturday afternoon, ’twere difficult to say; certain it is that when she found her way to the table close by the window and realized that he was not there, she felt conscious of an overwhelming sense of disappointment.  And yet during the whole of the week she had, with more pride than wisdom, avoided this particular A.B.C. shop.

“I thought you would not keep away very long,” said a quiet voice close to her ear.

She nearly lost her balance—­where in the world had he come from?  She certainly had not heard the slightest sound, and yet there he sat, in the corner, like a veritable Jack-in-the-box, his mild blue eyes staring apologetically at her, his nervous fingers toying with the inevitable bit of string.

The waitress brought him his glass of milk and a cheese-cake.  He ate it in silence, while his piece of string lay idly beside him on the table.  When he had finished he fumbled in his capacious pockets, and drew out the inevitable pocket-book.

Placing a small photograph before the girl, he said quietly: 

“That is the back of the houses in Phillimore Terrace, which overlook Adam and Eve Mews.”

She looked at the photograph, then at him, with a kindly look of indulgent expectancy.

“You will notice that the row of back gardens have each an exit into the mews.  These mews are built in the shape of a capital F. The photograph is taken looking straight down the short horizontal line, which ends, as you see, in a cul-de-sac.  The bottom of the vertical line turns into Phillimore Terrace, and the end of the upper long horizontal line into High Street, Kensington.  Now, on that particular night, or rather early morning, of January 15th, Constable D 21, having turned into the mews from Phillimore Terrace, stood for a moment at the angle formed by the long vertical artery of the mews and the short horizontal one which, as I observed before, looks on to the back gardens of the Terrace houses, and ends in a cul-de-sac.

“How long D 21 stood at that particular corner he could not exactly say, but he thinks it must have been three or four minutes before he noticed a suspicious-looking individual shambling along under the shadow of the garden walls.  He was working his way cautiously in the direction of the cul-de-sac, and D 21, also keeping well within the shadow, went noiselessly after him.