?" wondered Captain Jack
Benson, staring hard. "For I have seen him--somewhere. I'd declare
that under oath."

Figure, carnage and face all strangely haunted the submarine boy, who
crouched lower, watching.

"By the great turret gun! He's skulking for a reason!" muttered Benson.
"Is he spying on the mine-planting? I wonder? Yes! That must be his
work! Long-legs, I'll keep my eyes on you!"

The stranger hastened along for perhaps a quarter of a mile further.
Then he threw himself down on the sand, choosing a position in which he
could lie flat, his head fairly well hidden behind a low ridge of sand.

Unslinging the field-glass, the stranger brought it to his eyes, closely
watching the progress of the tug.

"Ha-ha!" muttered watchful Jack, who had followed, keeping behind
another sand ridge. "So, sir!"

The minutes passed, though Jack Benson was so absorbed in watching this
long stranger that the boy had but the vaguest notions of the flight of
time.

The tug had halted, now. A great crane at the bow swung around, and a
submarine mine hung poised in the air. Then, with a rattle of chains
not audible at the distance, the mine was slowly lowered until it
touched on bottom.

While this was going on, the long-legged stranger, wholly absorbed in
his own work, made some observations and some hurried calculations.
Then he pulled the drawing-board toward him, jotting down a point.

Jack Benson, standing stealthily, got a good look, for the first time,
at the top of that drawing board.

"A chart of the bay, of course," muttered Benson, savagely, between his
teeth. "The fellow is marking down the exact position of that mine!"

Still, the submarine boy did nothing to betray his own presence. He
watched and wondered. The thought struck him that this long-legged
one might be an officer of the Army, on observation duty like the
submarine boy himself.

"But that isn't right; I'm sure it isn't," decided young Benson, quickly.
"If they fellow were here on honest business, he wouldn't have sneaked
out here to get in position. Besides, I have a vague remembrance of
this fellow, and I don't connect him with anything honest!"

The Army tug, out on the bay, was now engaged in planting a second mine.
Again the slim stranger was all attention. When the crane began to
lower the mine, a second mark was made on the chart on the drawing
board.

Now, once more, the fellow lay at full length, watching intently off
ove