Nick did not say what he knew about him, nor of what his suspicions consisted. He saw that they already were entering the spacious grounds in which Mantell’s residence was situated, overlooking the Riverside Drive and the broad, glistening waters of the Hudson. "I suppose your father is downtown at this hour," he remarked, as the car sped up the driveway. "Yes. I dropped him at the surrogate court half an hour ago. Some of our business affairs are still unsettled. My wife and mother are here, however, though the latter is an invalid and confined to her room. To the side door, Greeley." The chauffeur bowed, and the limousine presently came to a stop under the massive porte-cochère protecting a side entrance to the imposing residence. Perkins, the butler, appeared almost immediately at the door. "Come in, Nick," Mantell said cordially, while they mounted the broad, marble steps. "We may find Helen in the library, or----” "Beg pardon, sir," said Perkins respectfully. "Mrs. Mantell has gone out." Mantell turned quickly. "Gone out!" he echoed. "Gone out with whom?" "With your father, sir." "With my father--nonsense!" "But, sir, I am very sure of it." "Impossible! When did she leave? How long ago?" Perkins glanced at a tall old clock in the hall. "Precisely half an hour, sir," said he. "I noticed the time." Mantell turned as pale as if suddenly death-stricken. "Half an hour!" he gasped, with affrighted gaze meeting that of the detective. "That is impossible, utterly impossible. Half an hour ago, Nick, I was with my father in the surrogate court." CHAPTER IV. THE CONNECTING LINK. Nick Carter already had come to two conclusions: One, that the miscreant by whom Helen Mantell had been repeatedly threatened was none other than Gaston Goulard. Another, that Gaston Goulard now had got in his iniquitous work. Nick saw, too, that Frank Mantell was in a fair way to collapse under the alarming discovery, and he at once took steps to encourage him. "You keep your head, Frank, and don’t let blind fear unman you," he commanded a bit sharply. "There is nothing in getting rattled. I know a good deal more about this matter than you suppose, and there is much less to fear concerning the personal safety of your wife than you imagine. Pull yourself together, therefore, and meet the situation man fashion. Let me take the ribbons, while you do as I have directed. I’ll speedily sift this to the bottom." All this, together with the detective’s strong personal influence, was not without effect. Mantell braced himself to meet the worst, saying quickly: "You are right, Carter, perfectly right. I must keep a grip on myself, or I shall go completely off my perch. What do you mean by saying that you know more about this matter than I suppose?" "I will presently tell you," said Nick. "Let’s get down to bare facts, for a starter, and I then will decide what must be done." "But what do you make of it? How could my father----”