What he had just witnessed was enough to make any experienced pilot think. Someone, flying a Nieuport, had a most novel way of treating with anti-aircraft gunners. He merely rolled over, straightened out, dipped twice, and the guns promptly left off their quarreling. No one could be stupid enough to reason that such manoeuver would discomfit the gunners, and yet in this case the effect was more efficacious than any manoeuver yet invented. McGee smiled at the stupidity of the thought. It was effective only because it was a signal, prearranged and understood by the anti-aircraft gunners. The pilot of that Nieuport was in communication with the enemy, and McGee believed that man to be Siddons! It all came to him in a flash. Who, better than Siddons, could have supplied the enemy with the information that brought them over to bomb the green squadron when they were stationed near Is-Sur-Tille? Someone supplied it, for Cowan had found in the pocket of the German flyer whom he, McGee, had brought down, an order disclosing the very fact that the raid had been planned on Intelligence reports. And where had Siddons gone that day after landing at Vitry on the slenderest excuse? The French Major said he had taken off within an hour. And the very next morning the squadron stumbled into a net spread by von Herzmann, and but for the timely and unexpected arrival of a large group of French Spads the harvest would have been great indeed. Could it be that Siddons had crossed the lines the previous afternoon, escaping Archie fire by a simple code of air signals, and disclosed the entire plan to the enemy? McGee felt a hot wave of ungovernable anger sweep over him. He no longer had any doubts whatsoever. Two and two make four. Siddons was a traitor to his country. To his country? No, doubtless he was one of the many who had been trained for years against this very hour of need. On false records he had gained admission to the American Air Force, and now-- McGee came out of the cloud into the clear sunlight, and began searching the sky for the Nieuport. It was not to be seen. He flew on, encountered other clouds, came out again, but the Nieuport had miraculously disappeared. McGee flew steadily northeast until he spotted an exceptionally large group of enemy planes, working up from the direction in which he was headed. It was time to turn around. He was quite too far into enemy territory to feel comfortable, and that swarm of planes made him unusually homesick, even though they were far below him. But just as he banked into a left turn he noticed that they were nosing down, sharply. He flew along the misty edge of a cloud, watching closely. Down, down, they went, becoming mere specks against the blue-grey ground haze.