But Fate decreed that he should act alone and without advice, and the intimation of Fate's intention came in the form of a short letter from Marcus Penn, asking for an interview. "I am confident," wrote the secretary, "that from what you threatened in the aeroplane you suspect me of knowing something relative to Sir Charles Moon's murder. As I am entirely innocent I resent these suspicions, and I wish you to meet me in order that they should be cleared away. If you will meet me at the booking-office of the Bakerloo Tube, I can take you to the person who gave me the perfume. He will be able to tell you that I have no connection with any criminal." Then the letter went on to state day and hour of the appointment, and ended with the feeble signature of the writer. Dan always thought that Penn's signature revealed only too plainly the weakness of his character. Of course he intended to go, even though he remembered that Penn had declared the identity of the person who had given him the perfume. His cousin in Sumatra had sent the same to him, the secretary had said, yet he now proposed to introduce Dan to another person, who was the donor of the scent. Unless, indeed--and this was possible--the Sumatra cousin had come to England with the intention of exonerating Penn. Certainly, Penn might mean mischief, and might be dexterously luring him to a trap. But Halliday felt that he was quite equal to dealing with a timid personality such as the secretary possessed. Also, when going to keep the appointment, he slipped a revolver into his hip-pocket, to be used if necessary. It might be--and Dan's adventurous blood reached fever heat at the mere idea--that Penn intended to introduce him to his brother scoundrels, who constituted this mysterious gang. If so, there was a very good chance that at last he might learn something tangible concerning the organization. Undoubtedly there was a great risk of his losing liberty if not life, and it was impossible to say what precautions this society of cut-throats might take to preserve its secrets. But Halliday was not of a nervous nature, and, moreover, was willing to risk everything on one cast of the die, instead of lingering in suspense. He therefore got himself ready without saying a word to any one, and kept the appointment. And, indeed, now that Laurance was absent, there was no one to whom he could speak. It chanced to be a somewhat foggy night when Dan descended to the underground in Trafalgar Square, but out of the darkness and in the light he had no difficulty in recognizing Penn. The secretary was well wrapped up in a heavy great-coat, and welcomed the young man with a nervous smile, blinking his pale eyes furiously, as was his custom when much moved. However, he spoke amiably enough, and appeared to bear no malice against his companion, notwithstanding the threat in the aeroplane.