A sound came from above. Harry groped toward the door. He was sure that he heard some one tapping. He listened. Single taps came at intervals. Harry tapped in return.
A quick, short message arrived in telegraphic code: “Hold out. Am working on lock.”
Harry replied: “The water is rising. Hurry.”
He did not know who his intended rescuer might be. It seemed improbable that Marquette could have returned. Possibly Professor Whitburn had discovered the situation.
He waited, and heard slight clicks from the other side of the door. He looked toward Arlette. The girl lay exhausted, her eyes closed.
Harry tapped: “Must save girl here with me.”
There was no reply. Then a sudden thought occurred to Harry. He tapped another message:
“Water coming through open sluices. They were opened after door closed. Must be controlled outside of this room.
The clicking sounds ended abruptly. Harry’s last piece of information had evidently given the rescuer an idea.
“Will seek sluice control,” came the message. “You can save girl.”