There is another little matter, too, which waits for your decision." "Tell me of it at once, please," she begged, with a sudden conviction of his meaning.
He obeyed without hesitation.
"I spoke just now," he reminded her, "of the three secret cities.

They are secret because we have taken pains to keep them so.

One is in Germany, one in Russia, and one in China.

A casual traveller could discover little in the German one, and little more, perhaps, in the Russian one.

Enough to whet his curiosity, and no more.