," flashed back Donald exultantly.

His fingers had hardly left the key before he was startled by a soft
footfall behind him.

The boy wheeled like a flash and then almost fell off his chair. Facing
him, with an ugly-looking revolver in his hand, was Barton, the
machinist.

There was a mean sneer on his sinister face as he snarled out:

"Let me see that message and let me see it quick."

"I've got no message for you," responded Donald, determined not to let
the man know that he had information of the green motor boat's
whereabouts.

"That's a lie," snarled Barton; "don't monkey with me. I've got this gun
and, jingo, I know how to use it, too."

CHAPTER XXIII.

THE DEPTHS OF OLD OCEAN.

Just as Donald, who was no match physically for the burly machinist, was
pondering what to do, the door which was open became filled by a rotund
figure.

It was Tubby.

In a jiffy he took in the scene, the threatening attitude of Barton, the
alarmed look of Donald, who stood staring at the revolver like a bird
fascinated by a snake. Tubby realized that it was no time for thinking
the situation over. Instead, he crouched low, and then, darting forward
with surprising agility, he seized the machinist around the legs before
the fellow knew what was happening.

Taken utterly by surprise, and borne off his feet by Tubby's rush,
Barton came crashing to the floor in a heap. As he fell the revolver
exploded, the bullet passing by Donald's head.

Barton struggled desperately with Tubby, but the stout youth held on to
him like a leech, at the same time yelling for help. In a few seconds
the ensign and Mr. Barr came rushing in, followed by the Boy Scouts and
the sailors. There was an end to the battle then and there. After a
brief resistance Barton, snarling and cursing, was tied hand and foot,
and the ensign ordered him locked up in the dining room shed for the
present.

Donald soon told his story and proudly exhibited the message from the
air which told of sighting the green motor boat. All agreed that it was
a cheering bit of news.

"If they were near a lot of islands when sighted, it is most probable
that they are hiding on one of the group. At all events, having the
latitude and longitude, it will be easy to go down there and see."

"What are you going to do about Barton? We have full proof of his
villainy now," struck in Merritt.

"I suppose we shall have to take him along with us. We can't waste time
going asho