"I suppose he never used a fountain pen?" asked The Thinking Machine.
"Not that I know of," the girl replied. "I have one," and she took it out of a little gold fascinator she wore at her bosom.
The scientist pressed the point of the pen against his thumb nail, and a tiny drop of blue ink appeared. The letter was written in black. The Thinking Machine seemed satisfied.
"And now the shop," he suggested.
Miss Devan led the way through the long wide hall to the back of the building. There she opened a door, which showed signs of having been battered in, and admitted them. Then, at the request of The Thinking Machine, she rehearsed the story in full, showed him where Stockton had been found, where the prussic acid had been broken, and how the servant, Montgomery, had broken in the door at her request.
"Did you ever find the key to the door?"
"No. I can't imagine what became of it."
"Is this room precisely as it was when the body was found? That is, has anything been removed from it?"
"Nothing," replied the girl.
"Have the servants taken anything out? Did they have access to this room?"
"They have not been permitted to enter it at all. The body was removed and the fragments of the acid bottle were taken away, but nothing else."
"Have you ever known of pen and ink being in this room?"
"I hadn't thought of it."
"You haven't taken them out since the body was found, have you?"
"I-I-er-have not," the girl stammered.
Miss Devan left the room, and for an hour Hatch and The Thinking Machine conducted the search.
"Find a pen and ink," The Thinking Machine instructed.
They were not found.
At midnight, which was six hours later, The Thinking Machine and Hutchinson Hatch were groping through the cellar of the Dorchester house by the light of a small electric lamp which shot a straight beam aggressively through the murky, damp air. Finally the ray fell on a tiny door set in the solid wall of the cellar.
There was a slight exclamation from The Thinking Machine, and this was followed immediately by the sharp, unmistakable click of a revolver somewhere behind them in the dark.
"Down, quick," gasped Hatch, and with a sudden blow he dashed aside the electric light, extinguishing it. Simultaneously with this there came a revolver shot, and a bullet was buried in the wall behind Hatch's head.
IV.
The reverberation of the pistol shot was still ringing in Hatch's ears when he felt the hand of The Thinking Machine on his arm, and then through the utter blackness of the cellar came the irritable voice of the scientist:
"To your right, to your right," it said sharply.
Then, contrary to this advice Hatch felt the scientist drawing him to the left. In another moment there came a second shot, and by the flash Hatch could see that it was aimed at a point a dozen feet to the right of the point where they had been when the first shot was fired. The person with the revolver had heard the scientist and had been duped.
Firmly the scientist drew Hatch on until they were almost to the cellar steps. There, outlined against a dim light which came down the stairs, they could see a tall figure peering through the darkness toward a spot opposite where they stood. Hatch saw only one thing to do and did it. He leaped forward and landed on the back of the figure, bearing the man to the ground. An instant later his hand closed on the revolver and he wrested it away.
"All right," he sang out. "I've got it."
The electric light which he had dashed from the hand of The Thinking Machine gleamed again through the cellar and fell upon the face of John Stockton, helpless and gasping in the hands of the reporter.
"Well?" asked Stockton calmly. "Are you burglars or what?"
"Let's go upstairs to the light," suggested The Thinking Machine.
It was under these peculiar circumstances that the scientist came face to face for the first time with John Stockton. Hatch introduced the two men in a most matter-of-fact tone and restored to Stockton the revolver. This was suggested by a nod of the scientist's head. Stockton laid the revolver on a table.
"Why did you try to kill us?" asked The Thinking Machine.
"I presumed you were burglars," was the reply. "I heard the noise down stairs and came down to investigate."
"I thought you lived on Beacon Street," said the scientist.
"I do, but I came here to-night on a little business, which is all my own, and happened to hear you. What were you doing in the cellar?"
"How long have you been here?"
"Five or ten minutes."
"Have you a key to this house?"
"I have had one for many years. What is all this, anyway? How did you get in this house? What right had you here?"
"Is Miss Devan in the house to-night?" asked The Thinking Machine, entirely disregarding the other's questions.
"I don't know. I suppose so."
"You haven't seen her, of course?"
"Certainly not."
"And you came here secretly without her knowledge?"
Stockton shrugged his shoulders and was silent. The Thinking Machine raised himself on the chair on which he had been sitting and squinted steadily into Stockton's eyes. When he spoke it was to Hatch, but his gaze did not waver.
"Arouse the servants, find where Miss Devan's room is, and see if anything has happened to her," he directed.
"I think that will be unwise," broke in Stockton quickly.
"Why?"
"If I may put it on personal grounds," said Stockton, "I would ask as a favor that you do not make known my visit here, or your own for that matter, to Miss Devan."
There was a certain uneasiness in the man's attitude, a certain eagerness to keep things away from Miss Devan that spurred Hatch to instant action. He went out of the room hurriedly and ten minutes later Miss Devan, who had dressed quickly, came into the room with him. The servants stood outside in the hall, all curiosity. The closed door barred them from knowledge of what was happening.