Escape from the Island of Aquarius by Frank Peretti

Book 2 of Cooper Kids Adventures

Summary: 

A cry for help from a sinking island…

A rescue mission leads Jay and Lila Cooper to a doomed South Sea island where nothing is as they expected. Instead of a primitive civilization, the Coopers encounter a busy colony with a mysterious leader claiming to be Adam MacKenzie, a missionary once presumed dead. To add to the confusion, someone seems to have pushed the island's self-destruct button. Earthquakes and erosion are tearing the island apart, and every moment is precious in the Coopers' search for the real Adam MacKenzie.

Escape from the Island of Aquarius is a page-turning tale of action, stolen identity, and nail-biting cliffhangers. You will not be able to put it down.

Opening Lines:

It was a hot, clear day on the South Pacific, and the ocean had that slow, lazy feel that could rock you to sleep with its gently rolling swells. The captain of the chugging trawler was bored and playing checkers with his first mate while another crewman stayed at the ship's wheel. There wasn't much to talk about, so nobody did much talking. They had hauled in their catch and were headed for port, and that was all that mattered.

Then the crewman at the wheel yelled, "Hey, Cap! There's something off the port bow!"