They walked on together, and Buck muttered in deep satisfaction: "I've spotted the man following us; a stout chap with a double chin and a look like a fat policeman out o' work. I reckon I've tumbled to this game. I've seen him outside our hotel." "Is it one of the gang?" asked Jack. "Oh, no," replied his companion. "More likely to be one o' these private detectives hired to watch us. Now we've got to throw pepper into his eyes, an' then make a break for the station." Buck raised his hand and hailed a growler. They got in, Buck said "Marble Arch," and away trotted the horse. Buck now set himself to keep a watch out of the little window at the back of the cab, and soon gave a chuckle of satisfaction. "He's coming," he said, "he's in a hansom about fifty yards behind. This makes it a dead cert that he's our man. It would be a bit too much of a coincidence for him to be outside our hotel last night, following us up Chancery Lane to-day, and now tracking us along Oxford Street." "How will you drop him?" asked Jack. "As easy as tumbling off a log," replied Buck. "We'll use Connaught Mansions. Do you remember its two entrances? We'll pop in at one and out at the other." Jack laughed, and understood at once. His father had a flat at Connaught Mansions, a huge block of flats near Lancaster Gate, which served as Mr. Haydon's London home between his journeys. They had made no use of it during the few days they had been in town, preferring a hotel near Mr. Buxton's rooms, but now it would be of service to their plans. As they neared the Marble Arch, Buck gave the address to the driver. He handed up a couple of half-crowns at the same time. "We may be detained at the place you're driving to," he remarked. "Wait a quarter of an hour at the door, and then if we don't send any message to you, you can go." "Very good, sir," said the cabby, and on rolled the growler, and soon turned into the courtyard of Connaught Mansions, and pulled up at the main entrance. Jack and his companion left the cab at once and went into the lobby, where the porter came out of his office. "Hullo, Mr. Risley, you are back again," said the porter. Then he caught sight of Jack, whose face was very well known from frequent visits to his father. The question which had plainly been on the porter's lips was at once checked. He had been eager to talk to Buck about the disappearance of Mr. Haydon, but Jack's presence put a barrier upon that. The cloppety-clop of the feet of a passing cab horse now came in through the open door of the vestibule. Jack glanced out and saw the stout man passing in his cab. The spy seemed to be very busy reading a paper, and the whole thing looked as innocent as could be.