Harry walked beside Mr. Bascomb, while Tom led the way with the treasurer.  Mr. Renshaw brought up the rear.

As the party came in sight of the beach and glanced out seaward, they saw many a little, dancing light out on the retaining wall.  Each light showed where a workman patrolled under the orders of Foreman Corbett.  The latter was aboard the motor boat, “Morton,” which ran up and down near the wall, throwing the searchlight over the scene.

“Reade,” remarked Mr. Prenter, “I don’t see that the enemy have any chance to-night to run in and work harm to our property.”

Hardly had the treasurer spoken when Tom, looking out seaward, saw a sudden, bright flash of light upward.  There was a brief pause—–­then the sullen boom of an explosion reached their ears.

“Mystery of all mysteries!” choked Tom Reade.  “There goes another section of the wall—–­blown up under our very eyes!”

CHAPTER XI

A MESSAGE FROM A COWARD

“Now Reade,” began President Bascomb, in a shaking voice, “what can you say—–­”

Tom didn’t wait to inform him.  The young chief engineer was darting out on the wall as fast as he could go.

Already the “Morton” had turned, and was chugging back to the scene of this latest outrage, the searchlight flashing back and forth, in the vain effort to detect any small craft stealing away from the vicinity.

“I—–­I can’t race on a narrow runway like that,” faltered Mr. Bascomb, halting at the beginning of the narrow wall.  “I—–­I’ll wait here, Mr. Renshaw, will you keep me company?”

“If you so direct, sir,” replied the superintendent.  “For that matter, what Reade and Hazelton can’t find out, out yonder, will probably never be discovered.”

“Do you share Mr. Prenter’s infatuation for those two young men?” asked the president of the Melliston Company.

“I can’t say about that, sir,” Renshaw replied, with a puzzled air.  “But this much I know—–­I never worked with two more capable men of any age.  They always know what to do, and they never lose their heads.”

Mr. Bascomb compressed his lips tightly.

In the meantime Tom, Harry and Treasurer Prenter covered nearly a quarter of a mile along the retaining wall when the motor boat, putting about, picked them up with the searchlight.

Toot! toot! sounded the boat’s pneumatic whistle.

“Foreman Corbett is signaling to us to wait and he’ll put in for us,” said Tom, coming to a halt.  Soon the motor craft chugged in alongside, coming close to the wall.  Tom, Harry and Mr. Prenter jumped, landing safely aboard.

“How did the enemy come to catch you napping, Corbett?” Tom inquired good-humoredly.

“They didn’t catch me napping, sir,” protested Foreman Corbett.  “It is the strangest thing, sir—–­that explosion.  Why, I had had my light turned on that very part of the wall at least a dozen times in the last half-hour before the blow-out came.  Our light didn’t pick up a soul around there at any time.  What do you suppose I did, Mr. Reade, as soon as the explosion sounded?”