When a few moments later he read the message sent him he was more than furious.

“Curse the luck!” he cried. “What stupidity in me! I ought to have held that fellow as a hostage. They will go and recover the gold themselves now. Up sails, men! Bear away at the tiller there! We must be the first to reach the spot. If the water is not too deep our diving suits will be as good as their boat.”

The Diver went down quickly to the bottom of the sea. No sooner, however, had the sandy bottom come into view than another peril presented itself.

A huge monster shot out of a dark defile.

It was the same giant fish which had attacked the boat once before. Frank saw him coming.

He at once suspected that this was the fellow who had dented the shell of the pilot-house. He saw the risk of another collision.

“Look out!” he shouted. “We may hit that fellow.”

In the stem of the submarine boat was a long steel ram. This was provided with electric communication with the dynamos.

Frank had foreseen just such an exigency.

He knew that if he could only strike the fish with this heavily-charged ram the trouble would be quickly over. The monster would be sure to succumb.