Mrs. Gentrie entered Mason’s private office with Junior trailing along behind her, very much as though he were being led.

Mrs. Gentrie’s attitude was one of parental indignation.

“Mr. Mason,” she said, “you’ll have to help us. It’s about Junior.”

Mason looked at the young man’s sullen features, and said, “Don’t tell me anything in confidence, Mrs. Gentrie, because, in a way, I’m not a free agent. It’s quite possible I won’t be able to help you.”

“Well, I’ve got to talk with someone, and I don’t know anyone else to whom I can turn. This thing has been preying on my mind ever since I heard what Junior said to the police. I thought at first my duty was to back up my son in a chivalrous attempt to protect some young woman’s good name. Then, when I began to think of how serious it might be because — well, because perhaps that murder is linked with — well, I can’t keep quiet any longer.”

“What’s eating you?” Junior demanded. “What’s got into you, Ma?”

She kept looking anxiously at the lawyer. “Don’t you think I’m doing the right thing, Mr. Mason?”

“Go ahead,” Mason said. “I’ve warned you.”

Young Gentrie spoke up to say, “You folks go ahead and talk about me all you please, but nothing anyone can do is going to change my position, or make me change my story. I want that definitely and finally understood.”

Mrs. Gentrie said, “I wish you’d try to impress on my son the importance of telling the truth, Mr. Mason.”

“Have you,” Mason asked the young man, “been taking liberties with the truth, Junior? Perhaps just fudging the least little bit?”

“No, I haven’t,” Gentrie said sullenly.

“Arthur, I know that you have. I tell you I heard that shot and got up. I looked in your room. You weren’t in your bed. You hadn’t been in your room.”

“Then you looked in before midnight. I got into my room at midnight, or just ten or fifteen minutes after.”

“I looked at the clock. It was thirty-five minutes past twelve.”

“You read it wrong. It was thirty-five minutes past eleven, and you thought it was thirty-five minutes past twelve. You didn’t have your glasses on, did you?”

Mrs. Gentrie said, “I didn’t have my glasses on, but I didn’t make a mistake in the time. I’m certain I didn’t. And everybody else says that was when the shot was fired.”

“What do you mean, everybody else?”

“Well, the other people in the house, all of them.”

Junior said, “Well, if you ask me, that fellow Steele is a phoney. I wouldn’t trust him as far as I could throw a loaded truck. Look at the way he’s always hanging around Rebecca, helping her with her crossword puzzles, stringing her along. What’s he really want, anyway? He isn’t supposed to be one of the family. He’s supposed to have a room rented, and that’s all. You know as well as I do Aunt Rebecca’s full of prunes, and she keeps her tongue rattling against the roof of her mouth all the time. It’s impossible to have any secrets around her. She spills everything she knows.”

“Junior, that’s not a nice way to talk about your Aunt Rebecca.”

Junior went on hotly, “The other night I was looking for my dictionary and couldn’t find it, and came downstairs to see if she had it, and she was telling him a whole lot of stuff about me. She hasn’t any right to do that.”

“You’re altogether too sensitive,” Mrs. Gentrie said. “She probably wasn’t talking about you at all.”

“The heck she wasn’t. I heard the whole business, all about how you were worried about me having an infatuation for an older woman. She said...” Junior’s voice suddenly choked up. His face changed color. “She said altogether too darn much,” he finished.

Mrs. Gentrie said, “Mr. Mason isn’t interested in our family squabbles, Junior. I came here because...”

“I’m old enough now to get out and get a job. I don’t need to work in Dad’s store. I’m worth the wages I’m getting from him and more. I can support myself. I’m a man now.”

Mrs. Gentrie turned to the lawyer, “I’m so worried,” she said. “Junior wasn’t in his room when that shot was fired. He keeps insisting that he was, but I know he wasn’t. Now, I understand that the police have found some fingerprints over in Hocksley’s flat, and I... well, I just wish Junior would tell the truth. That’s all. So I’d know what to expect.”

“You mean the fingerprints which were outlined in the paint?” Mason asked.

She nodded.

Junior said, “I tell you I was in bed.”

Mrs. Gentrie said, by way of explanation, “He’d been out with that stenographer, Opal Sunley, and he swears he took her home about midnight. I’m afraid, Mr. Mason, that he’s just doing it to — well, to give her sort of an alibi. Now you look here, Junior. You were just coming up the stairs to your room when that shot was fired, weren’t you? You took your flashlight and went sneaking down the stairs.”

Junior said, “I thought you said I wasn’t in my room.”

“You weren’t when I looked in there. The bed wasn’t even so much as wrinkled. But I’d heard someone sneaking along the corridor and on the stairs.”

“I tell you, you didn’t have your glasses on, and you made a mistake in the time.”

“But everybody says the shot was at twelve-thirty-five.”

“Phooey,” Junior said. “Because you didn’t have your glasses on and...”

“Then you think the shot was fired at eleven- thirty-five?” Mrs. Gentrie interrupted.

“Why, sure, if I wasn’t in my room... no, wait a minute... Yes, sure, that’s right. The shot was fired at eleven -thirty-five.”

She said, “Arthur, you’re stalling for time. You’re trying to think whether you can give her a good alibi for eleven-thirty-five.”

Arthur jumped to his feet. “Oh, let me alone,” he cried. “You make me tired! You’re always twisting everything I do so as to make it seem I’m trying to think of Opal. Can’t you leave her out of it ever?”

Mrs. Gentrie glanced at Mason.

Mason, without raising his voice, but putting the timbre of authority into his command, said, “Sit down, Arthur. I want to talk with you.”

Arthur’s eyes met the lawyer’s. The young man hesitated for a moment, then seated himself somewhat tentatively on the edge of a chair.

Mason said, “This is your first murder case. I’ve seen dozens of them. I don’t know very much about Miss Sunley. I’ve seen enough to know that you’re trying to protect her. Perhaps it hasn’t occurred to you that the most certain way to turn the limelight of pitiless, hostile publicity on her would be to twist the truth to try to keep her out of it.”

Arthur Gentrie was interested despite himself. “I don’t get you,” he said.

“You start suppressing or distorting facts to keep Opal Sunley out of that case,” Mason said, “and you’ll find that you’ve not only dragged her in, but have painted her with a crimson brush doing it.”

“What’s that crimson-brush crack?” Arthur Gentrie asked, suddenly belligerent.

Mason said, “Nice young men don’t tell lies in murder cases for nice young women. Do you get me?”

“I’m not certain that I do.”

“You make a good impression. The public would look on you as a nice young man. They would consider that the motivation which would cause you to lie to protect a woman would have to be more powerful and more compelling and, frankly, a little more sinister than the ordinary attraction which a nice young woman would or should have for you.

“Now, I’m not going to argue with you. I’m not going to plead with you. I’ve told you facts. If you want to drag Opal Sunley into this thing, if you want to smear her reputation, if you want the newspapers to treat her as an older woman who was leading a young boy around by the nose...”

Gentrie came up out of the chair as though he had been a fighter springing for an antagonist at the sound of the gong. “No, you don’t,” he shouted. “You can’t...”

Mason held up his hand, palm outward. Aside from that, he made no move. “Hurts, doesn’t it?” he said. “It hurts because you know it’s the truth. Now, what have you to tell me?”

“Nothing.”

Mason said, “All right, go on home. Get out. I told you I wasn’t going to argue with you, and I wasn’t going to plead with you. I’ve told you. There’s truth in what I’ve told you, and truth is an acid which burns through every falsehood. The only thing it won’t touch is the pure gold of unvarnished truth. My words are going to eat into your consciousness until they’ve cut through the falsehood and got down to the real truth. Then you’re going to make a clean breast of things, either to your mother or to me. And after that you’re going to feel better. Now, I’m busy. I haven’t time to discuss things further. Good-by.”

Gentrie, who had quite evidently braced himself when he was taken to the lawyer’s office for resistance against cajoleries and blandishments, appeared somewhat dazed by this abrupt dismissal. He said, “Why, I haven’t told any...”

Mason said, “I’m sorry, Gentrie. I haven’t the time to waste. Don’t bother to say anything more until you’ve had a chance to think over what I’ve said. Good afternoon, Mrs. Gentrie. Let me know if you want to see me again.”

Her eyes were troubled but grateful. “Thank you, Mr. Mason. Come, Arthur.”

Arthur hung back at the door, then suddenly squared his shoulders, pushed up his chin, and marched out, jerking the door behind him. He would have slammed it violently had it not been for the automatic door check.

Mason grinned across at Della Street. “Hot-headed youth on the rampage.”

Della Street said, “I thought he was going to hit you when you said what you did about Opal Sunley.”

“He was trying to make himself think so, too. At his age, it was what he considered the manly thing. Sometimes, Della, I don’t know but what hot-blooded, impetuous youth which has no time for weighing disadvantages against advantages, or consequences against acts, is a darn sight better than what we are pleased to call the mature outlook.”

Her eyes smiled at him. “Obey that impulse, eh?”

“Exactly,” he said.

She was laughing now. “Well, it’s a good idea. More the philosophy one would expect to hear in a taxicab driving home than in a law office. How about that code message?”

Mason said, “You would bring my nose back to the grindstone. Well, I’ll bite. What about the code?”

“Given it any thought?”

“Lots of thought, probably too much.”

“Look, Chief, if it’s a cipher, couldn’t you read it? There are nine words in the message, and I’ve always understood any cipher can be solved if there’s a long enough message.”

Mason said, “I guess that’s right, but I don’t think it’s an ordinary cipher in which letters are transposed.”

“Why not?”

“Let’s analyze this. There are nine words. Five of them begin with the letter c. The letter c is in every single word at least once.”

“Wouldn’t that indicate it was either e or a?”

“I’m afraid you’re missing the most significant thing about the whole message, Della.”

She studied the typewritten copy of the message which Mason pushed across to her. After an interval of silence, she said, “I’m afraid I don’t get it.”

“Look again. It’s relatively simple.”

“You mean that there are no short words in it?”

“That’s one thing,” Mason said. “The shortest word in there has five letters. The longest has six. That’s an interesting peculiarity of the message. Nine words. Three of them have five letters, and the other six have six letters. But there’s something that’s far more significant than that.”

“What?”

“Give up?” he asked banteringly.

She nodded.

“The last fourteen letters of the alphabet aren’t represented there at all,” he said. “The entire message is composed of words made up from the first twelve letters of the alphabet.”

Della Street frowned, stared down at the typewriting, then said thoughtfully, “That’s right. What does it mean?”

Mason said, “I’ll tell you one other significant thing. Every word contains either the letter a or the letter b.”

“I don’t see that that’s as important as the frequency with which the letter c occurs.”

“Perhaps not, unless we also consider positions. Every word has either a or b in it, but neither a nor b appears at the first of the word or at the ending. They’re always either the second or third letter from the end of the word.”

There followed an interval while she checked his conclusions, then nodded again.

Mason said, “That empty can is significant in a good many ways. I’m wondering whether Tragg has overlooked some of those things, or is just sitting tight and awaiting developments.”

“What, for instance?” Della asked.

“That can conveyed a message to some person,” Mason said. “That means two persons were concerned in the crime. That, in turn, means that the someone who put the can there must have had easy access to the basement. It also means that the person for whom the message was intended must have had easy access to the basement. Yet it also means that those two persons didn’t have access to each other. ”

“I don’t get you,” Della Street said.

“It’s simple,” Mason pointed out. “If the two persons could have met and talked with each other, there would have been no necessity for going to all that elaborate trouble of scratching a message in the top of the can, sealing the can, and placing it in the cellar.”

“Yes. That’s true.”

“The fact that the cellar was chosen as the place where the message was to be left means that both parties must have had access to the cellar.”

She nodded.

“Therefore,” Mason said, “we have a peculiar situation. Two persons have access to the same place, yet those persons don’t have contact with each other, and that place is highly unusual — the cellar of a big, rambling, frame residence.”

Della Street said excitedly, “Now that you analyze it, it’s plain as day. One of the persons had to have access to the cellar through the garage that Hocksley rented, and the other one because he lived in Gentrie’s house.”

Mason said, “That’s one of the possibilities.”

“But, Chief,” Della Street said, “that brings up all sorts of complications.”

“That’s just the point.”

“Then you think Junior is mixed up with it — and Opal?”

Mason said, “The evidence seems to point the other way.”

“What do you mean?”

He said, “Then the message in the can becomes perfectly meaningless... so far as the murder is concerned.”

“Why? Oh, I get it. Because he and she were together. Is that right?”

“That’s right.”

Della Street said with a smile, “Once that message is deciphered, it may turn out to be ‘I love you, darling, no matter what happens.’ Persons in love are inclined to do things like that, you know — or do you?”

Mason nodded, said, “Frankly, Della, if it had been a simple cipher where letters had been transposed in order to make a message, I would have been very much surprised if it had had anything to do with the murder. But as it is, I’m inclined to attach more importance to it. But the perfectly obvious and logical point seems to have escaped everyone.”

“What’s that?”

“The one real clue as to the identity of the person for whom the message was intended.”

“What’s the clue?”

Mason said, “The fact that only one person got it, of course.”

“You mean...?”

“Arthur Gentrie.”

“Junior? I thought you said he...”

“No, the father. He’s the one who went down in the cellar. He says he found the can lying in the box and opened it in order to mix up paint in it. Then he threw the top away, but you notice that when Steele became interested in the top, Gentrie saw that the tops were substituted. The one with the code message on it remained in the box, and one that had no message was put on the workbench.”

Della Street said, “My gosh, Chief, it’s perfectly obvious, now that you mention it. The way you sum it up, it sounds rather damning.”

Mason pulled the sheet of typewritten paper over to him, started studying it. Abruptly, he laughed.

“What is it?” she asked.

“That code,” he said. “It’s absolutely simple.”

“You mean you can read the message?” Della Street asked.

Mason nodded. “It’s absurdly simple when you approach the problem from the right angle.”

“What’s the right angle?”

“Notice,” Mason said, “that only the first twelve letters in the alphabet are employed. Notice that every word contains either a or b, and that a or b, whenever it appears, is either the second or the third letter from the end of the word. That, coupled with the fact that the words have either five or six letters, is absolutely determinative of the whole business. I wonder if Tragg has got it by this time.”

Della Street said, “I don’t get it.”

“Twelve letters,” Mason said. “Good Lord, Della, it fairly hits you in the face.”

“It doesn’t hit me in the face,” Della Street laughed. “It doesn’t hit me anywhere. I miss it altogether.”

Mason pushed back his chair. “I’m going out for fifteen or twenty minutes, Della. Think it over while I’m gone.”

She said, “Ordinarily, I’m a peaceful woman. I’m not given to homicidal mania, but if you arouse my curiosity this way and then try to go out of that door without telling me what the message says, I’m very apt to assault you with a deadly weapon before you get as far as the elevator.”

Mason said, “I don’t know what the message says.”

“I thought you said you did.”

“No. I said the solution was simple. Good Lord, Della, I can’t give you any more clues than that. I’ve virtually told you the whole thing now.”

“You’ll be back in twenty minutes?”

“Yes.”

“And you’ll tell me what the message says then?”

“Shortly afterwards, yes.”

“But I’m supposed to get the secret of this while you’re gone?”

“You should.”

“What does twelve letters have to do with it?”

“How much is twelve?” Mason asked.

She frowned. “You mean six and six?”

“That’s not it.”

“You don’t mean that since two and two make four, six and six make twelve?”

“No, not that way.”

“You mean it’s eleven and one?”

Mason smiled. “Try ten and two,” he said, “and you’ll be on the right track. And if you can’t get it from that, you’re going to have to buy me the drinks.”

Mason took his hat out of the coat closet, grinned at her, and started for the elevator.