"It has to be dipped into a solution; after that you can read it by heating. I have already dipped it into the solution. The moment the heat leaves the sheet the writing disappears again. The ink is waterproof. I'll show you." Jones got a candle from the mantel, lit it, and held the sheet of paper very close to the flame. Gradually, almost imperceptibly, letters began to form on the blank sheet. At length the message was complete. "Dear Hargreave--The Russian minister of police is at the Blank Hotel under the name of Henri Servan. He is investigating the work of the Black Hundred in this country and can free you from their vengeance if you supply the evidence needed." "Now, what evidence can he want?" asked Jim. "Such as will prove Braine an undesirable citizen." "And then?" "Quietly pack him off to Russia, where he is badly wanted." "Who sent this message?" "One of our mysterious friends. We have a few, as you already know. But I'll go and make this man Servan a visit. I have seen the real minister, and if this man is the same one, something of importance may turn up. I shall want you somewhere about. Here, I'll let you have this letter. Remember, heat brings it out and cold air makes it vanish. Now I'll go up for a moment to see how that poor girl is getting along. We are lucky; there's no gainsaying that." "You're a clever man, Jones," said Jim. Jones turned upon him, his face grave. The two men looked steadily into each other's eyes. Jones was first to turn aside his glance, as he had something to conceal and Jim had nothing. When the ambulance took the tortured Susan away, Jones addressed Florence gravely. "I am going out, and so is Mr. Norton. Do not leave the house; not even if you have a telephone call from me or Norton. Both of us will return; so don't let anything bother or confuse you." "I promise," said Florence, struggling with a sob. Jones went down-stairs again, paused by a window as if cogitating, and suddenly threw it up and looked abroad. A rustle among the lilacs caused a smile to flit across his face. So they had sent some one to learn the effect of the poison? Or to follow him should he leave the house? He retired to the kitchen and gave some explicit orders to the chef, orders which did not in any way refer to cooking. Then Jones and the reporter left the house, each quite aware that they were being followed. Near the Blank Hotel they separated in order to confuse the stalker. He might dodder and follow the wrong man. But it was evident that this time he had been directed to follow Jones; for he entered the hotel a minute after Jones.