"A periscope!" ejaculated the Flight-Sub.
"Let's hope it's one of our own submarines," said Ross.
"We'll soon find out," added his companion. "It's forging ahead. Whatever it is, they've got us under observation."
Jan, who was now on the bridge, had his attention called to the disconcerting fact. He beckoned to his two passengers.
"You had better go below and stow yourselves away," he suggested. "We will be boarded before long."
"Not I," replied the Flight-Sub. "They've marked us already. If they do take us they won't have to dig us out of a coal-bunker."
The submarine was emerging. At a pace that more than held its own with the Hoorn, she shook herself clear of the water, although green seas were breaking across the flat deck as far aft as the conning-tower.
Then muffled forms clambered through the hatchway; a young, yellow-bearded officer appeared on the navigation platform and hailed the Hoorn in Dutch to heave to instantly.
Even then the tough old Dutch skipper was not going to give in without a protest.
"For what reason?" he shouted back. "This is a Netherlands ship."