Della Street, humming a little tune as she opened the door to Mason’s private office, carrying the morning mail under her arm, stopped short with surprise, said, “Well, well, is this getting to be a habit?”

Mason grinned at her. “Come on over and sit down.”

She went back to close the door to the outer office. “What’s the idea?” she asked. “Been up all night?”

“No,” Mason said. “I got a few hours’ sleep. I guess that’s more than Drake did.”

“What happened?”

“A woman telephoned me about one o’clock in the morning, said she was Sarah Perlin, and she wanted to confess to the murder of R. E. Hocksley, wanted me to come at once to six-o-four East Hillgrade Avenue, said if she wasn’t there to wait until I saw a light, then open the back door and walk in. I took the precaution of telling Paul Drake to follow up in an hour if I didn’t telephone him everything was okay.”

“How did she get in touch with you?” Della Street asked.

“She called Paul Drake, and Paul held her on the line while he got in touch with me. I told Paul to give her my private number.”

“This was Mrs. Perlin, Hocksley’s housekeeper?”

“The voice said it was Mrs. Perlin. I don’t think it was.”

“Why not?”

“I think Mrs. Perlin was dead at the time. When I got out to the house on Hillgrade, I found her lying on the floor with a gun in her right hand and a bullet through her heart. It could have been suicide.”

“Did you report to the police?”

“Not directly,” Mason said. “I had other fish to fry. Opal Sunley came wandering in with a story that was just about as wild as mine. I didn’t realize how utterly incredible my story would sound to Lieutenant Tragg until I heard Opal Sunley telling me her version of about the same thing.”

“What did you do?”

Mason grinned. “I let Paul Drake hold the sack,” he said. “The hour was about up. Opal Sunley offered to play square if I wouldn’t notify the police, but give her a chance for a getaway.”

“Isn’t that compounding a felony?”

“It most certainly is — if she was guilty of a felony.”

“And how about not reporting the finding of the body?”

“I can get by with that in a pinch because I knew that Drake was on his way up. It only made a difference of a few minutes. The thing that bothers me is this Sunley woman.”

“What did you do with her?”

“Took her to a night spot and tried to get her tight.”

“Do any good?”

Mason shook his head. “She is a very bright young woman, or else I telegraphed my punch pretty badly. She started taking defensive measures even before I’d ordered the first drink.”

“What were the defensive measures?” Della Street asked. “I might have occasion to use them sometime.”

“Crackers and butter,” Mason said, “and lots of butter. She’d eaten about five squares before I got the first cocktail into her. After that, I knew it wouldn’t be much use.”

“Evidently the young woman knows her way around,” Della Street said.

Mason nodded. “I got her telephone number — Acton one-one-one-one-o.”

“What did she tell you about young Gentrie?”

“Not a great deal. Young Arthur Gentrie is madly in love with her. She’s older than he is and considers it a case of puppy love, but doesn’t want to destroy his illusions. She says that it’s very, very serious when a young man starts putting an older woman on a pedestal and becomes really infatuated for the first time in his life.”

“Is it the first time with Junior Gentrie?” Della Street asked.

Mason said, “He told her it was.”

“I don’t believe it.”

“He said there’d been puppy loves in his life before, but nothing that could approach the devastating effect of this feeling that he has for her.”

“And so she keeps on going out with him and encouraging him?”

“She says she isn’t encouraging him. She’s trying to be an older sister to him, but Junior won’t, as she expresses it, cool off. She said she had been trying to find some younger woman who would be sufficiently attractive to Junior to get his mind into what she calls a more normal state. The hell of it is, Della, she’s got a boy friend — some chap she’s crazy over — and she’s keeping all this about young Gentrie away from her regular boy friend because he’s insanely jealous. Of course, she’s also keeping all news of the boy friend from Gentrie because she doesn’t want to destroy his illusions.”

Della Street said, “It’s nice business if you can get it. How old is she?”

“Around twenty-two or twenty-three according to her looks, but something she said made me place her at about twenty-five.”

“What did Opal Sunley tell you about what happened in Hocksley’s flat?”

“According to her story, she arrived for work at the usual time in the morning, saw bloodstains, went out to look at the automobiles, saw that someone had been riding in the back of Hocksley’s automobile, and spilling blood. She couldn’t find either Hocksley or Mrs. Perlin. So she notified the police.”

“That’s all she told you?”

“Just about. I had to worm it out of her about her boy friend. I think that was the main reason she didn’t want the police to report her as having been in that bungalow at one-forty-five in the morning. Yet she was driving a borrowed car. I got the license number, of course.”

“The boy friend’s car?”

“No. Strangely enough it’s not. It belongs to a girl by the name of Ethel Prentice who is evidently a close friend of Opal’s — lets her take a jalopy in times of need.”

“Anything else?”

“Oh, she told a few things about her job over there. This man Hocksley was very much of a man of mystery, and so is Karr who lives in the flat above him. Somehow, that’s taxing credulity just a little bit too much. Two men of mystery drifting into an apartment house. They arrive within a week of each other, and, before that, the flats have been vacant for five months.”

“You think Karr and Hocksley have some connection?”

Mason shrugged his shoulders and said, “It’s rather a coincidence. Have you seen Karr’s ad in the paper?”

“No. What is it?”

“Opal Sunley told me about it — and said she noticed it because she’d seen Wenston’s name on the door of the other flat. It’s been running two days.”

Mason took the morning paper from the desk, opened it to the classified ad section, turned to the personals, and said, “Listen to this. ‘Personal. Wanted information concerning the daughter of the man who was a partner in a gun-running expedition up the Yangtze River in nineteen-twenty-one. Detailed information is purposely withheld from this advertisement, but the right party will know who I am, who her father was, and will be able to give proof of our association in the expedition in the fall of 1920, and the first part of 1921. I do not wish to be pestered, and, therefore, give warning that any imposter will be prosecuted to the limit of the law. On the other hand, the young woman who is the genuine daughter will be given a considerable sum of partnership assets which I have held for her in trust because I did not know until recently, and by accident, that my partner left any heirs at law. Do not seek to obtain an interview until after first writing Rodney Wenston, 787 East Dorchester Boulevard or telephoning Graybar 8-9351.’ ”

Mason finished reading the ad, pushed the newspaper to one side. Della Street pursed her lips. “Whew! And Opal Sunley told you about the ad?”

Mason nodded.

“I’d say that was rather significant, wouldn’t you?”

“Uh huh. Karr mentioned he started the ball rolling to clean up his partnership, but he didn’t mention this ad.”

“How did Opal happen to tell you about it?”

“Just talking.”

“What did she tell you about Hocksley?”

“Nothing much I didn’t know already. She got all of her work from wax cylinders. Hocksley dictated at night, and spent most of the day in bed.”

“Sleeping all day?”

“No. He’d be in his room. He’d get up along in the afternoon and read the papers, have coffee and toast, and sometimes do a little dictation.”

“To the machine?”

“Yes. Mrs. Perlin, the housekeeper, was the only one to go in and out of Hocksley’s room. She’d wait on him as soon as he wakened, bringing him the work Opal Sunley had typed, bringing out cylinders for Opal to transcribe, taking him his meals — the newspapers — sometimes sitting in there and talking with him. Opal could hear the hum of low-pitched conversation.”

“Any heart throbs between Hocksley and the housekeeper?” Della Street asked.

“Opal says she doesn’t know.”

“She considers it’s a possibility then?” Della Street asked.

“Apparently a very definite possibility.”

Della Street thought that over for a few seconds, then shook her head and said, “That isn’t right, Chief.”

“What isn’t?”

“That story of hers. No girl on earth would go on working for a man under those conditions without making it a point to learn more about him. In the first place, there’d be legitimate questions she’d have to ask about the work. In the second place, all that attempt to be secretive would simply arouse her curiosity.”

“Then you think she was lying to me?” Mason asked.

“I know darn well she was lying.”

Mason smiled reminiscently. “She did it most convincingly,” he said.

Della’s eyes were twinkling. “The hussy!”

Mason said, “Well, there’s no percentage in sitting around waiting for something to break. Why wouldn’t this be a fine time to communicate with the murderer?”

“Fine — but how are you going about it?”

“You could go down to a hardware store, Della, and buy a sealing machine for cans. Also get a new tin. We’ll scratch a message on the lid, seal it up, make certain there are no fingerprints on it, and plant it on the shelf at the Gentrie residence.”

“Think the murderer would get it?”

“It would be interesting to find out.”

“What sort of a message?”

“Oh, something that would tend to keep things moving,” Mason said. “We don’t want the case to get static. It would give the police too much of a chance to catch up on us.”

Della Street picked up the dictionary from Mason’s desk. “Think up a nice message, and I’ll put it in code for you.”

Mason said, “Well now, let’s see, Della. We want something that will get some action. Suppose we left the murderer a message. Let’s see. It will have to be dictionary words. We can’t use participles or plurals. We want something that will get swift action. Suppose we did this: ‘Lawyer Mason has fingerprint photograph his wallet fatal unless recovered.’ No, let’s see. We couldn’t use recovered. That’s past tense. The word in the dictionary would be recover.”

Della Street, frowning down at her shorthand notebook, said, “We could use recovery, Chief. That would be a noun, and would be listed. We could use the words recovery made instead of recovered.”

“Okay, let’s try putting it in code.”

“I don’t like the idea.”

“Why not?”

“It’s too much risk.”

“It’ll bring me into contact with the murderer.”

“That’s just it. The murderer will choose the time and the place of making the contact. He may even shoot first, and look in your wallet afterwards.”

“There’s always the chance,” Mason admitted, “but he’d be more apt to make a stick-up of it. And I’ll be careful.”

She said, “Yes, I’ve got a picture of you being careful — and when the murderer finds your wallet without a fingerprint in it, what...”

Mason walked across the office to a bookcase. On the top of this bookcase was a choice example of Japanese pigeon-blood cloisonne. He took a handkerchief from his pocket, polished the vase, ran his right hand through his hair several times, then pressed three of his fingertips against the surface. He said to Della, “Take that down to Paul Drake’s office. Have him develop the latent fingerprints on it, and photograph them. Don’t tell him why we want them. I’ll carry a copy of that photograph in my wallet. Then in case anything slips, the murderer won’t get suspicious.”

“Chief, I wish you wouldn’t do it. There’s no need for you to take the risk personally. Why not say that you have them in your office safe?”

“No. We can’t guard the office without letting someone else in on it. I want to handle this myself.”

“Why?”

“Because it won’t look like a trap then. But if I try to decoy the murderer into some office and have that office guarded, it’s going to look very much like a trap. The person with whom we’re dealing is far too intelligent to walk into so obvious a trap.”

Della Street reached for the dictionary. “Well,” she said, “I’ll put it in code. Only I do wish you wouldn’t do it, Chief.”

Mason said, “Here. Give me the dictionary. I’ll help you... ‘Lawyer.’ That’s in column a on page 569, the seventh word.”

Della Street spelled out the code word. “GHKAI.”

Mason turned through the pages again, said, “Isn’t it nice I have a name that’s listed in the dictionary?”

“You might wish it on Paul Drake,” she said. “We could use ‘Detective Drake’ just as well as ‘Lawyer Mason.’ ”

“No,” Mason said with a grin. “Paul isn’t feeling too friendly right now. He might object to being selected as the victim of a hold-up. At that, it’s a tempting thought. Detective Drake has an alliteration which is lacking in Lawyer Mason.”

“Shall we use it?” Della Street asked eagerly.

“No, absolutely not. Get thee behind me, Satan. Let’s get back to our knitting. Here’s Mason on the a part of page 615, the sixth word from the top.”

Della Street said, “Six-fifteen-A-six. That’ll be HCGAH. What’s next?”

Mason said, “I’ll look up ‘has.’ Let’s see. That’s the second word in column b on page 455.”

“That’s FGGBD.”

“Fine,” Mason said. “Now, ‘fingerprint.’ That’s page 377, the seventh word on the page.”

Della Street said, “Three-seven-seven-A-seven. That’ll be EIIAI.” Abruptly, she looked down at what she had written and began to laugh.

“What?” Mason asked.

“I was just wondering what would happen if Lieutenant Tragg got hold of this message,” she said. “Has it occurred to you, Chief, that out of four words, two of them have ended in AI?”

Mason frowned, scratched his head. “That isn’t so good,” he said. “It’ll give Tragg too much of a clue. He’ll know darn well then it isn’t just an ordinary cipher, but some sort of a code.”

“You don’t think he’ll get hold of this, do you?”

“He may.”

“I don’t see just what you’re planning to do. Won’t the man who gets the message know it’s a trap?”

“Not if my idea is correct. The persons who are using this means of communication both have access to that place in the cellar; but for some reason, they don’t dare to be seen talking together. Now if that’s the case, they won’t have any opportunity to clarify an ambiguity in the case. In other words, the person who gets the message can’t pick up a telephone and say, ‘Hello, Bill. I got your message. What do you mean, a fingerprint? Your fingerprint or my fingerprint. Or...’ ” Mason broke off suddenly to stare at Della Street. “Do you realize,” he demanded, “what I have just said?”

“About the telephone?”

“Yes.”

“What about it?”

“Why the devil should anyone resort to the complicated means of putting a code in the top of a can if he could get to a telephone? After all, you know, Della, my idea has been that the code idea was necessary because we had two persons who needed to communicate with each other, couldn’t see each other, and so had to leave messages in a can at a certain place.”

“Well, what’s wrong with that?”

“But why the devil couldn’t they telephone to each other? There wouldn’t be any danger in that. A person can go into a telephone booth anywhere, drop a nickel, dial a number, and talk with any person he wants. In that way, a man could give another complete instructions without the possibility of having them garbled, or, as happened in this case, having the woman of the house find the can and toss it into the discard.”

She frowned. “Well, why not?”

“That’s just it. There’s only one explanation. The person can’t use a telephone.”

“Why?”

Mason said, “Either because they can’t get to a telephone, or because they couldn’t use it if they did.”

“How do you mean?”

“Well, a deaf person couldn’t use a telephone.”

“Oh, I see.”

“And,” Mason said slowly, “a crippled person might not be able to get to a telephone.”

Della Street said, “Wouldn’t a crippled person have a telephone by the side of his bed? After all, a person who could put a can on a shelf, could certainly get to a telephone.”

Mason said, “There’s one person who doesn’t have a phone by his bed, yet is crippled. Remember Karr said he got so nervous at the sound of a bell he wouldn’t have a phone by his bed?”

Della said, “You’ve put your finger on something there.”

Mason stroked the angle of his jaw. “This begins to look like something,” he admitted. “But why should Karr communicate in code with anyone in the Gentrie house?”

“He’s the only one in the case who really couldn’t get to a telephone when he wanted one,” Della said.

Mason pursed his lips. “He is, for a fact. We’ll have to keep our eye on Mr. Elston A. Karr. It’s beginning to look very much as though he engineered the burglary of Hocksley’s flat. Of course, that doesn’t mean he suggested the murder of Hocksley.”

“Wouldn’t it make him legally responsible for it though — if he engineered the burglary?” Della Street asked.

“It would,” Mason agreed, a slight twinkle in his eyes, “on one condition.”

“What’s the condition?”

“That they can prove it on him.”

Della said, “You’ve just about done that by cold, remorseless logic.”

“I have, but that doesn’t mean Tragg’s going to. He may overlook that angle entirely.”

“Bosh! He pretends to be just dawdling along, and then— Wham!”

Mason abruptly walked over to the hat closet. “Be sure to get that can and the sealing machine, Della. Take that vase down to Paul Drake’s office. I’m going out to get a shave, a face massage, a manicure, and a quart of coffee.”

“I will,” Della Street said, then added, “and don’t you let that Sunley girl mix any more sex, simpers, and sweetness to kid you along.”

“You could have added pseudo-sincerity,” Mason grinned. “That also is alliterative.”

Della said, “Damn! I knew we shouldn’t have bought that dictionary.”