Kerry’s teeth snapped savagely together, and he chewed but made no reply, until: 

“There it is!” he said rapidly.  “On the marshes!”

A speck of light in the darkness it showed, a distant moving lantern on the curtain of the night.  Although few would have credited Kerry with the virtue, he was a man of cultured imagination, and it seemed to him, as it seemed to Seton Pasha, that the dim light symbolized the life of the missing woman, of the woman who hovered between the gay world from which tragically she had vanished and some Chinese hell upon whose brink she hovered.  Neither of the watchers was thinking of the crime and the criminal, of Sir Lucien Pyne or Kazmah, but of Mrs. Monte Irvin, mysterious victim of a mysterious tragedy.  “Oh, Dan! ye must find her! ye must find her!  Puir weak hairt—­dinna ye ken how she is suffering!” Clairvoyantly, to Kerry’s ears was borne an echo of his wife’s words.

“The traffic!” he whispered.  “If we lose George Martin tonight we deserve to lose the case!”

“I agree, Chief Inspector,” said Seton quietly.

The grating sound made by a boat thrust out from a shingle beach came to their ears above the whispering of the tide.  A ghostly figure in the dim light, George Martin clambered into his craft and took to the oars.

“If he’s for the Greenwich bank,” said Seton grimly, “he has a stiff task.”

But for the Greenwich bank the boat was headed; and pulling mightily against the current, the man struck out into mid-stream.  They watched him for some time, silently, noting how he fought against the tide, sturdily heading for the point at which the signal had shown.  Then: 

“What do you suggest?” asked Seton.  “He may follow the Surrey bank up-stream.”

“I suggest,” said Kerry, “that we drift.  Once in Limehouse Reach we’ll hear him.  There are no pleasure parties punting about that stretch.”

“Let us pull out, then.  I propose that we wait for him at some convenient point between the West India Dock and Limehouse Basin.”

“Good,” rapped Kerry, thrusting the boat out into the fierce current.  “You may have spent a long time in the East, sir, but you’re fairly wise on the geography of the lower Thames.”

Gripped in the strongly running tide they were borne smoothly up-stream, using the oars merely for the purpose of steering.  The gloomy mystery of the London river claimed them and imposed silence upon them, until familiar landmarks told of the northern bend of the Thames, and the light above the Lavender Pond shone out upon the unctuously moving water.

Each pulling a scull they headed in for the left bank.

“There’s a wharf ahead,” said Seton, looking back over his shoulder.  “If we put in beside it we can wait there unobserved.”

“Good enough,” said Kerry.

They bent to the oars, stealing stroke by stroke out of the grip of the tide, and presently came to a tiny pool above the wharf structure, where it was possible to lie undisturbed by the eager current.