Meanwhile, it is necessary to go back for a few moments to the garden and summer-house where Jack had been waiting, to see who was going to keep the assignation with Anstruther. On the whole, it was not unpleasant work, seeing that the night was very fine and warm, and at the same time dark and velvety. There were not many gardens in London as finely proportioned as those behind Barmouth's residence. It was wonderful, in the midst of that atmosphere, that flowers and shrubs could flourish so kindly. There were not many paths, most of the ground being given over to turf, so that Jack's feet made no noise as he walked along in the direction of the green gate which gave upon the lane beyond.

The gate turned out to be a door in the wall hidden from view inside by a deep belt of shrubs. It was here that Jack hid himself, and stood smoking his cigar with a determination to stay there all night if necessary. The best part of an hour had elapsed before there was a noise outside, and a hand turned the latch. Jack dropped his cigar, and ground it into the soft earth with the heel of his slipper. By this time his eyes had got accustomed to the darkness, so that it was not a difficult matter to make out the outlines of the approaching figure. The figure was that of a woman, evidently dressed for the evening, and wearing a mask.

Jack was not to be deceived; he knew that form perfectly well, even if he had not recognized the dress, which the wearer had used the night of his visit to Carrington's.

"Serena," he whispered to himself. "Well, I might have expected that. Now to see what will happen next."

Jack made his way hurriedly across the lawn, and took up a position behind a belt of pampas grass, where he could not only see into the summer-house, but also hear what was going on there. He was only just in time, for almost immediately the towering headdress of Anstruther appeared, and its owner made his way directly to the summer-house. Jack could see Serena as she hurried along. On the still night air every word could be distinctly heard. There came to Jack's ears a whispered apology from Serena that she was sorry for the delay.

"You might have ruined everything," Anstruther said savagely. "I told you to be here within half-an-hour at the latest."

Serena replied humbly that she could not get there before. She had to dress, and she had had to get the other servant out of the way. Anstruther muttered impatiently.

"I suppose it is impossible for a woman to keep to time," he said. "And now listen to me. There is something going on here which even I cannot fathom. I feel as if I were being laughed at; as if an unseen net was about my shoulders, and that a hidden hand was ready to close it at any time."

Jack listened eagerly to what followed. It was quite evident from what Anstruther said that Seymour's performance had made a deep impression upon him. For once in a way Anstruther was puzzled and frightened. He told Serena at considerable length all that had taken place during supper.

"There is more than meets the eye here," he said, "and that fellow said either too little or too much. One thing is quite certain--he is pretty intimately acquainted with my inner life in Mexico. Now who is he, and how does he know all this?"

"If you don't know, I can't tell you," Serena replied.

"No; but you are going to find out," Anstruther responded. "You are going to mingle with the other guests as if you were a friend of Lady Barmouth's, and I will sign to you presently what I want you to do. You have plenty of nerve and resource, and you must find some way of removing the mask from the face of my friend the magician. But that is not all. I have a very shrewd suspicion that this mysterious Lord Barmouth is no other than the man James Smith, who has been so useful to me from a pecuniary point of view."

"You think Lord Barmouth and James Smith are the same person?" Serena cried. "Oh, that is quite impossible."

"That remains to be seen," said Anstruther. "You know all about Lord Barmouth's reputation as a recluse as well as I do. Therefore, it will be part of your duty to get a sight of Lord Barmouth also. Mind you, I may be mistaken, but I have a strong impression that when you come to look at Barmouth you will see the features of James Smith. What the certainty of this means to me you can pretty well guess. Hitherto I have treated Smith as a comparatively poor man, never guessing for a moment that he was the enormously wealthy Barmouth, but in future----"

Anstruther paused significantly. The listener thrilled as he realized the danger in which Barmouth stood. But his whole attention now was concentrated upon Serena. He could see that she had drawn herself up to her full height; from the motion of her hands, she was evidently moved by some strong feeling. It flashed upon Jack all at once that Anstruther was asking Serena to plot against the happiness of her own sister--Lady Barmouth. That that was the chord that Anstruther had touched, Serena's first words proved.

"You are asking too much," she said . "I will not do it. There are times when I feel that this life of mine can endure no longer. I have worked hard for you; I have been the slave of all your schemes; I have forgotten that I possess a conscience."

"Yes; and you forget what you owe to me," Anstruther responded. "But for me you would long since have stood in a felon's dock. If you will think of the time when you and your boy----"

"No, no!" Serena cried. "I will not have it. What do I care if I alarm the people inside. For the sake of that black past I have consented to be your tool and slave. And yet I feel sometimes that you are playing with me; that the whole thing is nothing more or less than a cruel and deliberate lie on your part, and that my boy still lives. If I thought so; if I only thought so----"

Serena plunged forward, and Jack could see that something glittered in her hand. There was the confused suggestion of a struggle, the sound of an oath from Anstruther's lips, and the tinkle of metal upon the floor of the summer-house.

"So you have got one of your mad moods on to-night," Anstruther panted. "Do not push me to extremes, because you know what that means. Will you obey me or not?"

Jack could see Serena pass her hands across her eyes; he could hear the quick sobbing of her breath. "I was wrong," she said presently. It was marvelous how quickly she had recovered herself. "I will do your bidding. Let us go inside, and you can show me the man whose face you desire to see."

The two............