Judged by the theory they had worked out, the action of the men in the amphibian indicated that they were flying away with something they had found.

“If they had given up, so soon,” Dick mused, holding his head low to avoid the icy blast of their high position, “if they’d given up Jeff would go straight to the hangar again. But they’re going across Long Island Sound toward Connecticut, just as the unknown person in the hydroplane boat did with the other life preserver.”

Larry, holding speed at a safe flying margin so that the sustentation, or lifting power of the air, was greater than the drag of the airplane as it resisted the airflow, let the nose drop a trifle, let the engine rev down as he glided to a lower level where the air would not bite so much. They would be able to follow quite as well, dropping behind just enough to keep the line of distance between them as great as if they were higher and closer over the amphibian.
213

With his glasses, Dick could observe and indicate any change of direction or any other maneuver.

They had devised a hastily planned code of signals, very much like those used by a flying school instructor giving orders to a pupil where the Gossport helmet was not worn.

Dick, watchful and alert, lowered his chilled glasses and Sandy, keeping watch, saw his right arm extend straight out from his shoulder, laterally to the airplane’s course.

Sandy repeated the gesture after attracting Larry’s attention by a slight shaking of the dual-control rudder which was still attached, but which, on any other occasion, he had been careful not to touch.

“Left arm extended! Turn that way!” Larry murmured.

Gently he moved the stick to lower the left aileron, bringing up the right one, of course, by their mutual operation; rudder went left a trifle and in a safe, forty-five degree bank, he began to turn.
214

Almost instantly Dick again removed the chilly glasses, stuck his arm out ahead of him with his forearm and hand elevated, and motioned forward with the wrist and hand.

The signal was relayed by Sandy.

“Resume straight flight.”

Larry, getting the message correctly, reversed control, brought the airplane back to straight, level position on the new angle, and held it steady, revving up his engine and lifting the nose in a climb as Sandy gave him Dick’s sign, hand pointed straight upward, to climb.

“What in the world are they going to do?” he wondered.

“Have they discovered us?” Dick pondered the possibility.

“I can’t guess this one,” Sandy muttered. “They started to turn one way, then went on only a little off the old course, and now they’re coming up toward where we are.”

The problem was not answered, either by the continued gain in elevation or by the later change of plan.

“They’re gliding!”

Dick, as he made the exclamation, gestured with his arm toward the earth.
215

To Sandy’s signal Larry cut the gun, keeping the throttle open just enough to be sure the engine, in that chill air, would not stall, and with stick sent forward and then returned to neutral, imitated the gentle glide of the amphibian.

What it meant none of the three knew any better than did the half frozen caretaker who wished very sincerely that he had never come.

“Sandy! Sandy!” Dick cried as loudly as he could. “They’ve done a sharp turn—they’re going back home I think!”

Larry did not need to have the intricate signal relayed, nor did he wait to be told his passengers’ deduction. Their own maneuvers had given him a clue.

With the first change of direction and the following indecision that showed in the amphibian’s shifts of direction, Larry spelled a change of plan on the part of its occupants. The resulting glide, enabling his chums to speak above the idling noise of the engine, indicated a similar possibility in the other ship—Jeff and Mr. Whiteside were talking over plans.

He rightly decided that they had recalled sending the caretaker on a foolish errand. They must get back and make some explanation or he would suspect them, perhaps report............