“Then, quick, into the boat.”

They clambered down the wet ladder, and after an aggravating delay, the whirring engines of the racing craft were started.  Shirley took off his coat, and lashed a long rope about his waist.  He tied the other end of it securely to a thwart in the boat.

“What’s your idee, Cap?” asked the engineer, as he waited the signal.

“There’s a man trying to catch that white yacht out in the river.  I want to get him, that’s all.  If I fall out of this boat, keep right on going, for I’m tied up now.  Where’s the boat hook?”

“Here, sir.  Are you ready?  Just give me your directions.  All right, sir, we’re off.”

Shirley grunted and the hydroplane sped out onto the river, in a big curve, as he directed.  Like a white ghost on the river was the trim yacht, which even now could be seen speeding down the stream, all steam up.  There were two toots on the whistle and Shirley feared that his man had boarded her.  But the hydroplane, ploughing through the cold waves, whizzed toward the yacht, as he climbed out to the small flat stern.  A small boat had swung close to the yacht now.  A ladder had been lowered from a spar, while a man standing in the little craft missed it.  The yacht was gliding past the boat, when another rope ladder was deftly swung over the stern.

The hydroplane was close up now, and Shirley saw his prey dangling at the end of the ladder, now in the water, struggling with the rungs of the ladder, and now being drawn up.

His engineer, with a skilful hand on the helm, swung in close to the yacht, as keen for the capture as his patron.  They whizzed past at almost railroad speed, and Shirley, sprang toward the ladder.  His arms closed about the body of Reginald Warren in a grip which he braced by a curious finger-lock he had learned in wrestling practice.

Two revolvers barked over the taffrail of the yacht, as the hydroplane raced onward, dragging Shirley and his prisoner at the end of the rope, through the water.  Again the shots rang out, but they were out of range, on the dark waters so quickly, that before the police boat had set out from shore to investigate the firing from the pleasure vessel, the criminologist’s struggle with his wounded antagonist was over.

Half drowned, himself, with Warren completely past consciousness, Shirley was pulled into his own boat as the engines were slowed down.  They returned rapidly to the dock.

“Help me work him—­that was a pretty rough yank.  He’s been shot in the hand already.”

They rolled Warren on a barrel, “pumped” his arms, and by the time the Cronin automobile had returned with the other detectives, Warren was restored to understanding again.  Shirley forced some liquor between his teeth, to be greeted with a torrent of strange oaths.

“The jig is up, Warren,” said the criminologist.  “As a chess-player in the little game, you are a wonder.  But, I think I may at last call ‘Checkmate.’”