"What did Douglas Keene say when you told him?"

"Douglas Keene said he thought it was evidence of the greatest importance. He asked me a lot of questions about where the different pipes led, and wanted to know if the pipe into which the tube was running ran up to Peter Laxter's bedroom."

"Did it?"

"I think it did."

"Then what?"

"He advised me to tell the authorities what I'd seen."

"Did you do it?"

"Not yet. I was waiting for… a friend… I wanted to get his advice before I did anything which would cause trouble."

"What time was this that you encountered Sam Laxter in the garage?"

"About half past ten, I guess."

"That was several hours before the fire."

"Yes."

"Do you know whether Sam came in the house immediately after that?"

"No, I don't. I was so angry when he made that crack I walked out to keep from slapping him."

"But he must have returned to the house before the fire because he was in pajamas and robe when you were aroused by the fire."

"Yes, that's so."

"And he was fully clothed when you saw him there in the car?"

"I think so, yes."

"Now, you say that you turned on the lights?"

"Yes. Why?"

"The lights in the garage were off?"

"Yes."

"The door was closed?"

"Yes."

"Then the last person driving a car into that garage must have closed the door behind him, is that right?"

"Yes, of course."

"And the light switch was near the small door."

"Within a few inches of it. Why?"

"Because," Mason said slowly, "if Laxter had driven his car into that garage, he must necessarily have left the car, gone to the garage door, closed it, switched off the lights and then returned to his own car. After all, one doesn't drive cars into garages through closed doors."

"Well, what of it?"

"If he was so drunk he couldn't shut off the motor, but was just sprawled over the wheel, letting the motor run, it would hardly seem possible he'd have been able to get up, close the garage doors, switch out the lights and return to his car."

She nodded slowly.

"I hadn't thought of that."

"You're expecting this friend who is going to advise you what to do?"

"Yes, he's due at any minute."

"Would you mind telling me his name?"

"I don't think that needs to enter into it."

"Is it Frank Oafley?"

"I refuse to answer."

"And you aren't going to tell the authorities about this unless your friend tells you to?"

"I'm not going to commit myself on that. I'm not putting myself entirely in this friend's hands. I'm only asking him for advice."

"But you feel that in some way the fire was started through the exhaust fumes?"

"I'm not a mechanic; I don't know anything about automobiles. I don't know anything about gas furnaces. But I do know there's a flame in that gas furnace all the time, and it seemed to me if the mixture in the carburetor had been rather rich and some gasoline fumes had been thrown into the furnace, they might have exploded and started a fire."

Mason yawned ostentatiously, glanced at Drake and said, "Well, Paul, I guess that isn't going to help us much. There's no way those exhaust fumes could have started a fire."

She looked from one to the other with disappointment on her face.

"Are you sure?"

"Positive."

"Then why was the hose running from the exhaust to the pipe in the heating outfit?"

Mason countered with another question. "There was only one light in the garage?"

"That's right—a very brilliant light which hung in the center of the garage."

"Don't you suppose it's possible what you saw was a rope instead of a hose?"

"Absolutely not—it was some sort of flexible tubing—that is, the outside of it looked like flexible rubber tubing, and it ran from the exhaust of Sam Laxter's car to a hole which had been cut in the heating pipe. It's a big heating pipe, you know, covered with asbestos. The hot air goes up through there, into Pete Laxter's bedroom and sitting room."

Mason nodded thoughtfully. "Tell you what I'll do," he said. "I'll look around a little bit and if you decide to tell your story to the authorities I may be able to help you get in touch with some of the members of the homicide squad who aren't quite as skeptical and hardboiled as Sergeant Holcomb."

"I'd like that," she said simply.

"Well," Mason told her, "we'll think it over and give you a buzz, if we get any new ideas. In the meantime, you can let us know what your friend advises you to do. If you decide to tell the authorities, let us know."

She nodded slowly. "Where can I reach you?"

Mason took Drake's arm and, by a gentle pressure, pushed him toward the door. "We'll call you back later on tonight. Simply swell of you to have talked with us," he told her.

"It wasn't an ordeal at all," she said, smiling. "I was glad to tell you all I knew."

In the corridor, the detective looked at the lawyer.

"Well," Mason said, chuckling, "the cat stays."

"So I gathered," Drake observed. "But I don't see just how you're going to play your cards."

Mason led the detective to the end of the corridor, lowered his voice almost to a whisper.

"When next I see my esteemed contemporary, Nat Shuster, I'll ask him to read Section 258 of the Probate Code, which provides, in effect, that no person convicted of murdering a decedent shall be entitled to succeed to any portion of the estate, but the portion that he would be entitled to shall go to the other heirs."

"Let's see if we figure the mechanics of this thing the same way," Drake said.

"Sure we do," Mason answered. "It's dead open and shut. The hotair gas furnace had a lot of pipes leading to different rooms in the house. Each of those pipes had a damper, so that heat could be shut off from the rooms which weren't in use. Sam Laxter committed murder by a very simple process. He drove his car into the garage, clamped flexible tubing to his exhaust pipe, tapped a hole in the pipe which sent hot air to Peter Laxter's bedroom, and closed the damper back of the place where he'd brought the tubing into the pipe. Then he sat in his car, running the motor. Deadly monoxide gas from the automobile exhaust went through the flexible tube into the heating pipe, and was carried into Peter Laxter's bedroom.

"Notice the diabolical cleverness of the thing: He had only to let his motor run in order to bring about a painless death in a room many feet removed from the motor behind locked doors. Then he set fire to the house. Carbon monoxide is normally found in the blood of persons who have expired in burning buildings. It was a beautiful case of murder, and apparently the only witness is this redheaded nurse who caught him in the act, and the only reason she's alive today is that Sam Laxter thinks she doesn't realize the significance of what she saw. Or perhaps he doesn't know she saw the tube leading from the exhaust to the pipe."

The detective pulled a stick of chewing gum from his pocket, and said, "What do we do next?"

"We get in touch with the district attorney," Mason replied. "He's always claimed that a criminal lawyer uses his intelligence to keep murderers from paying the penalties of their crime. Now I'm going to fool him by showing him a perfect murder case I've uncovered, where his own men have fallen down on the job."

"It seems like such a thin skeleton of evidence on which to hang a murder accusation," the detective objected.

"There's nothing thin about it," Mason retorted. "Notice that the time was about quarter past ten at night. It had been dark for several hours. The garage doors were closed. Sam Laxter pretended he'd been drunk when he brought his car into the garage. But he must have left the car, gone to the sliding doors, closed them, and then climbed back in the car and kept the motor running. He must have attached the flexible tubing to his exhaust pipe and then must have arranged to feed it into the pipe which ran to his grandfather's room. Then all he had to do was to start the motor. Probably he didn't need to keep it running very long. If I remember my forensic medicine correctly, the exhaust gas of motor cars produces carbon monoxide at the rate of one cubic foot per minute per twenty horsepower. The average garage can be filled with deadly fumes in five minutes from running an ordinary automobile. Exposure to an atmosphere containing as little as twotenths of one percent of the gas will cause a fatal result in time. The post mortem indications are a bright, cherryred blood. The gas affects the blood so that it can't distribute oxygen to the tissues, and these indications are customarily found in the blood of one who has died in a burning house.