Up came that plate again and out popped Andy Greggs, armed with a pistol and a short knife.
The young lieutenant slipped into the water like an eel and dove down almost out of sight, to come up near to Oscar's feet.
The Japanese were half asleep, thinking their prisoner secure.
With cat-like steps Andy left the water, pushed through the bushes and came up behind Oscar.
Two slashes of that sharp knife and the young captain of the new Holland was free.
He slid behind the tree, and side by side he and Andy ran for the ocean.
"Hi-cha-kling!" roared one of the Japanese soldiers, rousing suddenly, and then he aimed his rifle at Oscar.
But before he could pull the trigger Andy fired his pistol, which had been kept dry on the journey to shore, and the bullet pierced the enemy's heart.
Before the other Japanese could do anything both of the chums were swimming for the Holland. They tumbled into the trap-door one after the other and then the plate was slid shut.
"Down!" ordered Andy, and immediately the submarine craft sunk several feet. Then a swift run was made for a third of a mile away from the coast.