The latter turned on his chum angrily.

"What do you mean by that?" he demanded. "Have you turned coward, that
you surrender to a couple of Germans without a fight?"

"I haven't turned crazy," replied Jack quietly. "They are too many for
us; that's all."

The other boat came alongside now and an officer stepped aboard the
boys' craft.

"Your weapons," he said in perfect English.

"Then please step aboard my boat. You shall be taken to Gravesend at
once."

"Gravesend!" echoed Jack. "You couldn't take us to a better place. But
if you are German, why should you take us there?"

"German," repeated the man. "You know we are English. You are the German
spies."

"No such thing," declared Frank, taking a hand in things. "We are
British officers and we thought you were German spies. That's why I
fired at you. We thought you were here to learn the secret of the
vanishing submarines."

"Frank!" cried Jack in warning, but it was too late.

"The vanishing submarines, eh?" repeated the stranger. "So you have