“I should think you would have had enough adventures on the Mexican border,” he said, “to last you the rest of your lives. Yet here you are lamenting because you can’t have more. Besides, this matter can be of no particular concern to you.”

“Just the same,” said Frank, “it is. We have a personal interest in the matter. We started it by overhearing the plotters. Then we found this inventor with his sound detector that probably will enable the Secret Service to locate the smugglers’ radio plant and secret cove. Now we are calmly shouldered out of the way. It’s hard luck, as Bob says.”

Mr. Temple smiled tolerantly.

“You can’t expect me to sympathize with you very much,” he said. “Well, now, which shall it be? The theatre or a prowl around Chinatown?”

Chinatown? In a moment the pessimism of the boys vanished. They were all smiles.

“Chinatown by all means,” said Jack, emphatically.

“Righto,” agreed Bob.

“With its opium dens and hatchet men and gambling clubs and all,” declared Frank.

“Oh, it isn’t what it used to be,” deprecated Mr. Temple. “I understand Chinatown is quite civilized now. Nevertheless, I expect we shall find much to interest us. I’ll speak to the head waiter. Probably he can direct us to a guide.”

On being consulted, the head waiter agreed to obtain them a guide. Presently, the boys and Mr. Temple were on their way by auto to the unique city within a city which constitutes San Francisco’s Chinatown, a quarter housing more than 30,000 Chinese. Oriental in every characteristic, with narrow alleys and courts, cellars, sub-cellars and sub-sub-cellars, the dragon roofs of Chinatown lie just below Nob Hill, the old aristocratic quarter of San Francisco with its veritable palaces of stone. From the terraces of the latter, one can look down into the alleys of Chinatown. So close neighbors are these two opposite districts of the city by the Golden Gate.