O’Connor at the last moment had to withdraw and let us go alone, for the worst, and not the unexpected, happened in his effort to clean up Chinatown.  The war between the old rivals, the Hep Sing Tong and the On Leong Tong, those ancient societies of troublemakers in the little district, had broken out afresh during the day and three Orientals had been killed already.

It is not a particularly pleasant occupation cruising aimlessly up and down the harbour in a fifty-foot police boat, staunch and fast as she may be.

Every hour we called at a police post to report and to keep in touch with anything that might interest us.  It came at about two o’clock in the morning and of all places, near the Battery itself.  From the front of a ferry boat that ran far down on the Brooklyn side, what looked like two flashlights gleamed out over the water once, then twice.

“Headlights of an automobile,” remarked Craig, scarcely taking more notice of it, for they might have simply been turned up and down twice by a late returning traveller to test them.  We were ourselves near the Brooklyn shore.  Imagine our surprise to see an answering light from a small boat in the river which was otherwise lightless.  We promptly put out our own lights and with every cylinder working made for the spot where the light had flashed up on the river.  There was something there all right and we went for it.

On we raced after the strange craft, the phantom that had scared Staten Island.  For a mile or so we seemed to be gaining, but one of our cylinders began to miss—­the boat turned sharply around a bend in the shore.  We had to give it up as well as trying to overtake the ferry boat going in the opposite direction.

Kennedy’s equanimity in our apparent defeat surprised me.  “Oh, it’s nothing, Walter,” he said.  “They slipped away to-night, but I have found the clue.  To-morrow as soon as the Customs House is open you will understand.  It all centres about opium.”

At least a large part of the secret was cleared, too, as a result of Kennedy’s visit to the Customs House.  After years of fighting with the opium ring on the Pacific coast, the ring had tried to “put one over” on the revenue officers and smuggle the drug in through New York.

It did not take long to find the right man among the revenue officers to talk with.  Nor was Kennedy surprised to learn that Nichi Moto had been in fact a Japanese detective, a sort of stool pigeon in Clendenin’s establishment working to keep the government in touch with the latest scheme.

The finding of the can of opium on the scene of the murder of Bertha Curtis, and the chase after the lightless motor boat had at last placed Kennedy on the right track.  With one of the revenue officers we made a quick trip to Brooklyn and spent the morning inspecting the ships from South American ports docked in the neighbourhood where the phantom boat had disappeared.