The Sultan of the Sulu Sea

Having found the sunken Japanese ship, the Hana-Maru in the South China Sea, the Wallace Boys and Singaporeans, Kheng Peng and Zainal, are about to head for home, when Moro pirates from the Sulu Sea give chase to their yacht, the Silver Spray.

Despite all their attempts to elude their foe, the Silver Spray is caught.

Rather than allow their yacht to fall into the hands of their captors, the boys decide to scuttle her at the first opportunity with tragic consequences.

The two Wallaces are taken to the pirates' island lair in the middle of the Sulu --Sea to be held for ransom.

With no one to rescue them, it looks as though this is the end of the line for the brothers.