Sir Reginald sat on the edge of the table and whimsically regarded his former subordinates. At that moment, rising above the staccato rattle of the pneumatic hammer, came the unmistakable whirr of an aerial propeller. To Kenyon and Bramsdean it was much the same as a trumpet-call to an old war-horse.

"Sounds like old times, eh?" remarked Sir Reginald.

"Rather, sir," agreed Kenyon heartily, and, at a loss to express himself further, he relapsed into silence.

"Experimental work, sir?" enquired Bramsdean.

Fosterdyke nodded.

"Yes," he replied in level tones. "Experimental work, that's it. That's why I sent for you. I'm contemplating a flight round the world. Keen on having a shot at it?"

[CHAPTER II--FOSTERDYKE EXPLAINS]

The two chums were not in the least taken aback with the announcement. They knew the way of their late O.C. On active service Fosterdyke was in the habit of issuing orders for certain operations to be performed without apparently considering the magnitude or the danger of the undertaking. The officer or man to whom the order was given almost invariably executed it promptly. In the few cases where the individual instructed to carry out a "stunt" failed to rise to the occasion, that was an end of him as far as his service under Wing Commander Sir Reginald Fosterdyke went. Fosterdyke had no use for faint-hearted subordinates.

On the other hand, Kenyon and Bramsdean were astonished at being invited to take part in what promised to be the biggest aerial undertaking ever contemplated. After nearly two years "on the ground" the prospect of "going up" seemed too good to be true.

"Business difficulties, perhaps?" hazarded Fosterdyke, noting the faint signs of hesitation on the part of the two chums. "Think it over. But I suppose you'd like to have a few particulars of the stunt before committing yourselves?"