Detective-Sergeant Coombes and three assistants watched the house of Sin Sin Wa, and any one of the three would have been prepared to swear “on the Book” that Sin Sin Wa was sleeping. But he who watches a Chinaman watches an illusionist. He must approach his task in the spirit of a psychical inquirer who seeks to trap a bogus medium. The great Robert Houdin, one of the master wizards of modern times, quitted Petrograd by two gates at the same hour according to credible witnesses; but his performance sinks into insignificance beside that of a Chinese predecessor who flourished under one of the Ming emperors. The palace of this potentate was approached by gates, each having twelve locks, and each being watched by twelve guards. Nevertheless a distinguished member of the wizard family not only gained access to the imperial presence but also departed again unseen by any of the guards, and leaving all the gates locked behind him! If Detective-Sergeant Coombes had known this story he might not have experienced such complete confidence.  
That door of Sin Sin Wa's establishment which gave upon a little backyard was oiled both lock and hinge so that it opened noiselessly. Like a shadow, like a ghost, Sin Sin Wa crept forth, closing the door behind him. He carried a sort of canvas kit-bag, so that one observing him might have concluded that he was “moving.”
 
Resting his bag against the end wall, he climbed up by means of holes in the neglected brickwork until he could peer over the top. A faint smell of tobacco smoke greeted him: a detective was standing in the lane below. Soundlessly, Sin Sin Wa descended again. Raising his bag he lifted it lovingly until it rested upright upon the top of the wall and against the side of the house. The night was dark and still. Only a confused beating sound on the Surrey bank rose above the murmur of sleeping London.
 
From the rubbish amid which he stood, Sin Sin Wa selected a piece of rusty barrel-hoop. Cautiously he mounted upon a wooden structure built against the end wall and raised himself upright, surveying the prospect. Then he hurled the fragment of iron far along the lane, so that it bounded upon a strip of corrugated roofing in a yard twice removed from his own, and fell clattering among a neighbor's rubbish.
 
A short exclamation came from the detective in the lane. He could be heard walking swiftly away in the direction of the disturbance. And ere he had gone six paces, Sin Sin Wa was bending like an inverted U over the wall and was lowering his precious bag to the ground. Like a cat he sprang across and dropped noiselessly beside it.
 
“Hello! Who's there?” cried the detective, standing by the wall of the house which Sin Sin Wa had selected as a target.
 
Sin Sin Wa, bag in hand, trotted, soft of foot, across the lane and into the shadow of the dock-building. By the time that the C.I.D. man had decided to climb up and investigate the mysterious noise, Sin Sin Wa was on the other side of the canal and rapping gently upon the door of Sam Tuk's hairdressing establishment.
 
The door was opened so quickly as to suggest that someone had been posted there for the purpose. Sin Sin Wa entered and the door was closed again.
 
“Light, Ah Fung,” he said in Chinese. “What news?”
 
The boy who had admitted him took a lamp from under a sort of rough counter and turned to Sin Sin Wa.
 
“George came with the boat, master, but I signalled to him that the red policeman and the agent who has hired the end room were watching.”
 
“They are gone?”
 
“They gather men at the head depot and are searching house from house. She who sleeps below awoke and cried out. They heard her cry.”
 
“George waits?”
 
“He waits, master. He will wait long if the gain is great.”
 
“Good.”
 
Sin Sin Wa shuffled across to the cellar stairs, followed by Ah Fung with the lamp. He descended, and, brushing away the carefully spread coal dust, inserted the piece of bent wire into the crevice and raised the secret trap. Bearing his bag upon his shoulder he went down into the tunnel.
 
“Reclose the door, Ah Fung,” he said softly; “and be watchful.”
 
As the boy replaced the stone trap, Sin Sin Wa struck a match. Then, having the lighted match held in one hand and carrying the bag in the other, he crept along the low passage to the door of the cache. Dropping the smouldering match-end, he opened the door and entered that secret warehouse for which so many people were seeking.
 
Seated in a cane chair by the oil-stove was the shrivelled figure of Sam Tuk, his bald head lolling sideways so that his big horn-rimmed spectacles resembled a figure 8. On the counter was set a ship's lantern. As Sin Sin Wa came in Sam Tuk slowly raised his head.
 
No greetings were exchanged, but Sin Sin Wa untied the neck of his kit-bag and drew out a large wicker cage. Thereupon: “Hello! hello!” remarked the occupant drowsily. “Number one p'lice chop lo! Sin Sin Wa—Sin Sin....”
 
“Come, my Tling-a-Ling,” crooned Sin Sin Wa.
 
He opened the front of the cage and out stepped the raven onto his wrist. Sin Sin Wa raised his arm and Tling-a-Ling settled himself contentedly upon his master's shoulder.
 
Placing the empty cage on the counter. Sin Sin Wa plunged his hand down into the bag and drew out the gleaming wooden joss. This he set beside the cage. With never a glance at the mummy figure of Sam Tuk, he walked around the counter, raven on shoulder, and grasping the end of the laden shelves, he pulled the last section smoothly to the left, showing that it was attached to a sliding door. The establishments of Sin Sin Wa were as full of surprises as a Sicilian trinketbox.
 
The double purpose of the timbering which had been ad............