“Did he keep any record of his cases?”

“Of course!  He was most particular.  Cadby was a man with ambitions, sir!  You’ll want to see his book.  Wait while I get his address; it’s somewhere in Brixton.”

He went to the telephone, and Inspector Ryman covered up the dead man’s face.

Nayland Smith was palpably excited.

“He almost succeeded where we have failed, Petrie,” he said.  “There is no doubt in my mind that he was hot on the track of Fu-Manchu!  Poor Mason had probably blundered on the scent, too, and he met with a similar fate.  Without other evidence, the fact that they both died in the same way as the dacoit would be conclusive, for we know that Fu-Manchu killed the dacoit!”

“What is the meaning of the mutilated hands, Smith?”

“God knows!  Cadby’s death was from drowning, you say?”

“There are no other marks of violence.”

“But he was a very strong swimmer, Doctor,” interrupted Inspector Ryman.  “Why, he pulled off the quarter-mile championship at the Crystal Palace last year!  Cadby wasn’t a man easy to drown.  And as for Mason, he was an R.N.R., and like a fish in the water!”

Smith shrugged his shoulders helplessly.

“Let us hope that one day we shall know how they died,” he said simply.

Weymouth returned from the telephone.

“The address is No.—­Cold Harbor Lane,” he reported.  “I shall not be able to come along, but you can’t miss it; it’s close by the Brixton Police Station.  There’s no family, fortunately; he was quite alone in the world.  His case-book isn’t in the American desk, which you’ll find in his sitting-room; it’s in the cupboard in the corner—­top shelf.  Here are his keys, all intact.  I think this is the cupboard key.”

Smith nodded.

“Come on, Petrie,” he said.  “We haven’t a second to waste.”

Our cab was waiting, and in a few seconds we were speeding along Wapping High Street.  We had gone no more than a few hundred yards, I think, when Smith suddenly slapped his open hand down on his knee.

“That pigtail!” he cried.  “I have left it behind! 
We must have it, Petrie!  Stop!  Stop!”

The cab was pulled up, and Smith alighted.

“Don’t wait for me,” he directed hurriedly.  “Here, take Weymouth’s card.  Remember where he said the book was?  It’s all we want.  Come straight on to Scotland Yard and meet me there.”

“But Smith,” I protested, “a few minutes can make no difference!”

“Can’t it!” he snapped.  “Do you suppose Fu-Manchu is going to leave evidence like that lying about?  It’s a thousand to one he has it already, but there is just a bare chance.”