sland, so that the Brant house was on
high land, too. On the north side, the land sloped down toward the
boat landing.

Rick stood on the edge of the low cliff and looked for Barby and Jan.
They weren't in sight.

"They must be using lungs," Scotty said. "Watch for bubbles."

No bubbles were visible, either. Rick checked carefully and began to
worry. It was a calm day with little wave action, and the bubbles from
the lungs should have been clearly visible. Surely they wouldn't swim
so far the bubbles couldn't be seen on a day like this.

"Let's check," Rick said.

The boys hurried to the room where the Scuba equipment was kept. Two
lungs and the blue and white equipment were gone. So was the cart. A
quick look at Pirate's Cove showed no cart in sight.

Where could they have gone? The boys hurried to the front of the lab
building again and found Joe Blake still getting a bit of sunshine.

"Did you see the girls?" Rick asked hurriedly.

Joe nodded. He motioned across the island. "They came and got
aqualungs and hauled the cart across to the north side. They're
probably swimming over there."

Rick doubted it. He doubted it very much. The currents on the north
side kept the bottom stirred up and visibility was too poor for
diving.

Without the need of exchanging a word, Rick and Scotty were suddenly
running. As they passed the house Rick had a sudden thought. He went
in and ran up the stairs to his room, grabbed his radio unit and
turned it on.

"Barby!" he called frantically. "Barby!"

There was no answer. Tucking the unit into his pocket, he ran out and
joined Scotty again. If Barby had her set she wasn't using it.

"Come on." He led the way to the boat cove and stopped short. The
speedboat was there, and so was the Scuba cart, but the rowboat
wasn't. Anxiously he scanned the water. There was no sign of the
girls.

Where were they? Where? The thought struck him. He remembered Barby's
comment of the night before.

_Had they gone to the houseboat?_

CHAPTER XVII

Pointer to Disaster

Scotty ran to the speedboat and yelled, "Come on!"

"Wait!" Rick called. "Let's not go barging off without knowing what
we're doing."

Scotty turned, puzzled. "What do you mean?"

"The girls have some kind of plan, and we don't know what it is. If we
go barging around in the speedboat, we might throw a monkey wrench
into the works."

"But we can't just stand here and do nothing," Scotty said
desperately.