Dorothy’s experiences, since she had shopped for neckties for her father that morning had been quite enough to lay up the average girl for a week, and to wreck her nerves into the bargain. Laura Lawson’s appearance in her bedroom had strained tightened nerves to the breaking point.

The arrival of this second intruder was just too much. As the butler stepped out of the closet and started to close the door, Dorothy’s self-control snapped like a rubber band. She forgot that she was playing a part; that it might be suicidal to show her hand so early in the game. Fear gripped her throat. Had this man been sent to kill her? If not, then what was he doing, stealing into her room through a secret entrance like an assassin of the middle ages? Self-preservation bade her act. The consequences could take care of themselves.

“Stop!” The harsh whisper, as her hand dove for Flash, sounded like the voice of a stranger. “Move another step, and I’ll pin you to that door!” Flash was in her raised hand now, the extended blade reflecting the light in the closet as though the polished steel were glass.

She saw the man start in surprise and turn his head in her direction. As she was about to hurl the knife, Tunbridge found his voice.

“Ashton Sanborn sent me, Miss Dixon. Please don’t throw that knife.”

Gone was the English accent, and the pompous intonation of the British man servant. Tunbridge, if that were really his name, spoke the American Dorothy was accustomed to hear, the accents of the cultured New Englander. For the second time in her life, Dorothy fainted.

She awoke to find herself in bed. Tunbridge was beside it. She could just make out his tall, powerful figure in the darkness.

“Goodness—did I faint?” she said weakly.

“You certainly did, Miss Dixon.” His tone was little above a whisper. “Please don’t raise your voice—and drink this. I found the aromatic spirits of ammonia in the bathroom. You need something to steady you. No one is cast iron—you’ve been through a frightful lot today.”

Dorothy took the glass and drained it. Then she lay back on her pillow. “I got the scare of my life just now. Why didn’t Ashton Sanborn tell me about you, Mr.—”

“Tunbridge is really my name, Miss Dixon. John Tunbridge, and very much at your service. I was afraid my rather abrupt appearance would startle you, and especially coming so soon after Mrs. Lawson’s—er—visit. I got a shock myself when I saw your white figure by the door just now, and all ready to split me with that knife, like—like a macaroon.” He chuckled, and removing the tray, sat down on the chair beside her bed.

“Oh, then you’ve seen Ashton Sanborn this evening, Mr. Tunbridge?”

“Heard from him, Miss Dixon. As you must know by now, I am a secret service operative and I am working under Mr. Sanborn. There isn’t time to go into detail now, but a couple of months ago, our department received an anonymous letter saying that Doctor Winn would bear watching. Shortly before that the Doctor had engaged Mrs. Lawson, who is an expert chemist by the way, to take charge of his laboratory. Her husband has been Doctor Winn’s secretary since last spring. We thought at that time that Mrs. Lawson might be the mysterious letter writer. Since then we’ve altered our opinion. Mr. Sanborn decided that inasmuch as Doctor Winn was working for the government it would be well to have a secret service man in the house. We prevailed upon the butler here to resign and I took his place.”

“Then Doctor Winn knows you’re a government detective?”

“No one in this house knows that, except you, Miss Dixon. The whole matter was arranged through an employment agency. Doctor Winn and the others here have no idea that I, like you, am simply playing a part.”

“Well, you’re certainly a splendid actor, Mr. Tunbridge.”

“Thank you, Miss Dixon. As you’ve no doubt discovered, acting, convincing acting, often plays a large part in our profession. You are doing brilliantly in that respect yourself. Mr. Sanborn thought, however, that it would be better if you did not know about me until the necessity arose. Mrs. Lawson, he knew would be watching you like a hawk when you arrived. If you had been aware of my identity, your position would only have been more difficult. She might have had her suspicions aroused in some way, which would have given you a wrong start from the beginning. I think you will realize tomorrow how hard it will be to treat me as though I were merely Tunbridge the butler.”

“Oh, I think you’re right. Tell me, how did you find out about the lemonade?”

“I overheard the Lawsons talking, yesterday. Made it my business in fact. It seems that Mrs. Lawson has had the idea that if Janet Jordan was only shamming sleep at that meeting, she would do her best to communicate with her father in some way. The natural thing to do would be to write a note and slip it in his hand or his pocket, when he came to see her. Martin Lawson was sure he would detect anything of the kind when he brought Jordan to say goodbye to Janet tonight at the flat. If not, the plan was to drug the girl with hot lemonade so that Mrs. Lawson could search her belongings for the note tonight.”

Dorothy nodded. “I watched her closely while she was in here, and so far as I could make out she didn’t find anything that interested her particularly. The Lawsons must have guessed wrong about Janet writing her father.”

“Well, no, they didn’t,” declared her new ally. “Janet wrote a letter, just as they surmised.”

“But where could it be?” asked Dorothy in a startled whisper, and sat bold upright in bed.

“Probably destroyed by this time,” Mr. Tunbridge chuckled. “There’s no need to worry on that score, Miss Dixon. When Ashton Sanborn spoke to your cousin this afternoon by means of Howard Bright’s headphone set, he learned that Janet proposed doing just what this clever pair here figured upon. Of course she had already written the note, and as there was no safe way to get rid of it in her room, he told her to take it with her when she left. And now if you’ll be good enough, I wish you’d tell me what happened after you took her place in the flat.”

Dorothy gave him a short sketch of her encounter with her uncle and Martin Lawson in Janet’s room, and of the conversation between the two men in the corridor afterward. “All the way up here,” she ended, “I pretended I had a grouch. Mr. Lawson tried to start a conversation several times, but he soon found it wasn’t much fun talking to himself and he gave it up as a bad job.”

“Excellent,” applauded the secret service man, “and quite in keeping with your behavior in the flat. You have done most remarkably well, Miss Dixon. Only—you won’t mind if I warn you not to let first success make you careless.”

“Do you really believe that these people mean to do away with me if they discover I am not what I appear to be, Mr. Tunbridge? It sounds a bit too melodramatic, don’t you think?”

“These Lawsons, husband and wife, are playing for gigantic stakes.” The detective’s voice, though barely audible was extremely grave. “They will stop at nothing. When crooks have at least two murders behind them, they’re not likely to stop at a third.”

“Then—then they are not what they pretend?”

“Certainly not. They’re a pair of high class European crooks named duVal.”

Dorothy shuddered. “And murderers!”

“Undoubtedly. They’re wanted both in England and in Austria for their crimes.”

“How did you find that out?”

“Oh, you see I recognized them when I arrived here, Miss Dixon.”

“But—but I can’t see why—why you didn’t arrest them then and there! You knew that they were after the secret of Doctor Winn’s new explosive, or whatever it is he has invented.”

“Yes, we realized that the formula for Doctor Winn’s explosive gas was the magnet that drew the du Vals to this house; but until today we had no idea how they proposed to dispose of the formula after stealing it.”

“I see. And now you realize that they probably intend to sell it to the organization of which my uncle is a member?”

“You are right, Miss Dixon.”

“Then why can’t you arrest the Lawsons now?”

“We can take the Lawsons at any time,” Tunbridge explained. “But we want to catch the ringleader of this organization. We know the group exists and for no good purpose, but what their definite object may be we still have no means of telling. We can’t arrest them on suspicion alone. Once they actually buy the formula from the Lawsons, it will be quite a different matter.”

She shook her head slowly. “But why hasn’t the formula been stolen before this? They’ve had plenty of opportunity, surely—”

“Because it is not completed. At dinner tonight I heard the Doctor say that by tomorrow afternoon the work would be finished, and that he expected to take the formula to Washington the day after tomorrow.”

“Then you expect?—”

“I expect that the Lawsons will make their attempt tomorrow night.”

“And where do I come in on this business, Mr. Tunbridge?”

“You are going to take the plans from Doctor Winn’s safe before the Lawsons get to it.”

She drew her breath sharply. “That’s a pretty large order—”

“I know it, but—of course you’ll have the combination of the safe—”

“Are you going to give it to me now?”

“Too dangerous. They are quite capable of searching your belongings again—or your person, for that matter—at any time. I’ll get it to you with exact instructions just as soon as the Doctor completes that blooming formula and locks it in the safe.”

“That’s all very well, Mr. Tunbridge. But has it occurred to you that if I steal this paper—I suppose it will be a paper?—”

“Probably several of them—”

“Well, if I take these papers before the Lawsons can get them, how are you going to arrest my uncle and the other men?”

“You,” directed Tunbridge, “will simply make a copy and replace the original documents where you found them. This is a safety-first move. We must have a copy in case the originals are destroyed.”

“It looks like a very complicated matter to me,” Dorothy admitted candidly. “Why not put the old gentleman wise? After all, it’s his formula, and if he made his own copy it would save us a possible run-in with the Lawsons, and—”

Mr. Tunbridge stood up. “Perhaps you’re right,” he said, making a brave attempt to stifle a yawn, “but Doctor Winn would never agree to it. For a scientist who dabbles in high explosives, he’s the most nervous man I’ve ever met. He’d give the whole show away. No, that’s out of the question. Doctor Winn must be kept in ignorance of the whole proceeding. And now—” a yawn got the better of him this time— “and now to bed. You need sleep even more than advice just now. Good night, or rather, good morning, Miss Dixon. Pleasant dreams, I hope.”

He started toward the door and Dorothy sprang out of bed and reached for her dressing gown.

“I want to see that secret passage, Mr. Tunbridge,” she said in a low tone.

“Oh, yes, come along.” He opened the door and stepped inside the closet. “It works this way. Press your foot on the board in the farthest right hand corner, like this, and a panel in the back wall slides up—like that—”

Dorothy stared at the gaping black hole, then as the detective-butler snapped on his flashlight she saw that a narrow circular staircase led downward in the wall.

“That stair curves down to the ground floor,” he explained. “It comes out through the side wall inside the big fireplace in the hall. To open the panel down there you press a button under the left-hand corner of the mantel. To close either panel you simply put it down, once you’re inside.”

“Are there any more of these passages in the walls?”

“Very likely, but I haven’t found them yet. Winncote is an exact copy of the Doctor’s ancestral home in Wales. Those old houses were honeycombed with priest holes, secret passages and whatnot. And Doctor Winn had his architect copy the original Winncote across the water down to the last stone, with modern improvements such as bathrooms and steam heat, added.”

“Funny old fellow, isn’t he?” commented Dorothy sleepily. “Then I’m simply to carry on until I hear from you again?”

“That’s right. But whatever you do, watch your step with the Lawson woman. She is fully as heartless as she is beautiful. If you had never heard of that meeting in the Jordans’ flat, it would be much better for you. She will try to trap you, so please be on your guard continually. Well, good night, again.”

“Good night, Mr. Tunbridge.”

The panel in the back wall of the closet slid into place, and Dorothy went back to bed. She realized now that this matter of impersonating her cousin was not going to prove to be the easy job she had fancied. A slip on her part now would not only put her own life in danger, it would probably ruin all government plans to apprehend these desperate criminals.

At last she fell into a troubled sleep wherein she dreamed that a long circular staircase curved round and round her bedroom, and that Mrs. Lawson, dressed as a butler, had set her to watch every step of it.