Robert Cairn entered a photographer's shop in Baker Street.
 
"You recently arranged to do views of some houses in the West End for a gentleman?" he said to the girl in charge.
 
"That is so," she replied, after a moment's hesitation. "We did pictures of the house of some celebrated specialist—for a magazine article they were intended. Do you wish us to do something similar?"
 
"Not at the moment," replied Robert Cairn, smiling slightly. "I merely want the address of your client."
 
"I do not know that I can give you that," replied the girl doubtfully, "but he will be here about eleven o'clock for proofs, if you wish to see him."
 
"I wonder if I can confide in you," said Robert Cairn, looking the girl frankly in the eyes.
 
She seemed rather confused.
 
"I hope there is nothing wrong," she murmured.
 
"You have nothing to fear," he replied, "but unfortunately there is something wrong, which, however, I cannot explain. Will you promise me not to tell your client—I do not ask his name—that I have been here, or have been making any inquiries respecting him?"
 
"I think I can promise that," she replied.
 
"I am much indebted to you."
 
Robert Cairn hastily left the shop, and began to look about him for a likely hiding-place from whence, unobserved, he might watch the photographer's. An antique furniture dealer's, some little distance along on the opposite side, attracted his attention. He glanced at his watch. It was half-past ten.
[200]
 
If, upon the pretence of examining some of the stock, he could linger in the furniture shop for half-an-hour, he would be enabled to get upon the track of Ferrara!
 
His mind made up, he walked along and entered the shop. For the next half-an-hour, he passed from item to item of the collection displayed there, surveying each in the leisurely manner of a connoisseur; but always he kept a watch, through the window, upon the photographer's establishment beyond.
 
Promptly at eleven o'clock a taxi cab drew up at the door, and from it a slim man alighted. He wore, despite the heat of the morning, an overcoat of some woolly material; and in his gait, as he crossed the pavement to enter the shop, there was something revoltingly effeminate; a sort of cat-like grace which had been noticeable in a woman, but which in a man was unnatural, and for some obscure reason, sinister.
 
It was Antony Ferrara!
 
Even at that distance and in that brief time, Robert Cairn could see the ivory face, the abnormal, red lips, and the long black eyes of this arch fiend, this monster masquerading as a man. He had much ado to restrain his rising passion; but, knowing that all depended upon his cool action, he waited until Ferrara had entered the photographer's. With a word of apology to the furniture dealer, he passed quickly into Baker Street. Everything rested, now, upon his securing a cab before Ferrara came out again. Ferrara's cabman, evidently, was waiting for him.
 
A taxi driver fortunately hailed Cairn at the very moment that he gained the pavement; and Cairn, concealing himself behind the vehicle, gave the man rapid instructions:
 
"You see that taxi outside the photographer's?" he said.
 
The man nodded.
 
"Wait until someone comes out of the shop and is driven off in it; then follow. Do not lose sight of the cab for a moment. When it draws up, and wherever it draws up, drive right past it. Don't attract attention by stopping. You understand?"
[201]
 
"Quite, sir," said the man, smiling slightly. And Cairn entered the cab.
 
The cabman drew up at a point some little distance beyond, from whence he could watch. Two minutes later Ferrara came out and was driven off. The pursuit commenced.
 
His cab, ahead, proceeded to Westminster Bridge, across to the south side of the river, and by way of that commercial thoroughfare at the back of St. Thomas' Hospital, emerged at Vauxhall. Thence the pursuit led to Stockwell, Herne Hill, and yet onward towards Dulwich.
 
It suddenly occurred to Robert Cairn that Ferrara was making in the direction of Mr. Saunderson's house at Dulwich Common; the house in which Myra had had her mysterious illness, in which she had remained until it had become evident that her safety depended upon her never being left alone for one moment.
 
"What can be his object?" muttered Cairn.
 
He wondered if Ferrara, for some inscrutable reason, was about to call upon Mr. Saunderson. But when the cab ahead, having passed the park, continued on past the lane in which the house was situated, he began to search for some other solution to the problem of Ferrara's destination.
 
Suddenly he saw that the cab ahead had stopped. The driver of his own cab without slackening speed, pursued his way. Cairn crouched down upon the floor, fearful of being observed. No house was visible to right nor left, merely open fields; and he knew that it would be impossible for him to delay in such a spot without attracting attention.
 
Ferrara's cab passed:
 
"Keep on till I tell you to stop!" cried Cairn.
 
He dropped the speaking-tube, and, turning, looked out through the little window at the back.
 
Ferrara had dismissed his cab; he saw him entering a gate and crossing a field on the right of the road. Cairn turned again and took up the tube.
 
"Stop at the first house we come to!" he directed. "Hurry!"
[202]
 
Presently a deserted-looking building was reached, a large straggling house which obviously had no tenant. Here the man pulled up and Cairn leapt out. As he did so, he heard Ferrara's cab driving back by the way it had come.
 
"Here," he said, and gave the man half a sovereign, "wait for me."
 
He started back along the road at a run. Ev............