The trade wind whistled through the rigging as the Sulu Crest cleared the reef barrier outside Bongao harbor. Below the waterline, the sonar screen painted a jagged trench four hundred meters deep—deeper than any government survey map recorded.
Clara adjusted the frequency gain. A distinct geometric echo pulsed back from the seabed, repeating every nine seconds like a steady heartbeat.
“That’s not a volcanic reef,” said Captain Aris, squinting through the helm glass. “Reefs don’t produce ninety-degree angles.”
Clara secured the waterproof datapad into her harness. “Ready the submersible. We dive before the patrol boats catch our radar signature.”