"Sounded like a ghost, didn't it?" he asked.

"Ghosts don't rattle papers," snapped Preston. "At least self-respecting ones don't, and the other kind haven't any right to run around loose. So suppose we try to trap this one."

"Trap it? How?"

"Like you'd trap a mouse--only with a different kind of bait. Is there any milk in the house?"

"Possibly--I don't know."

"Go down to the refrigerator and find out, will you? I'll stay here until you return. And bring a saucer with you."

A few moments later, when the chief returned, bearing a bottle of milk and a saucer, he found Preston still standing beside the table, his eyes fixed upon a corner of the room from which the sound of rattling paper had come.

"Now all we need is a box," said the Postal operative. "I saw one out in the hall that will suit our purposes excellently."

Securing the box, he cut three long and narrow strips from the sides, notched them and fitted them together in a rough replica of the figure 4, with the lower point of the upright stick resting on the floor beside the saucer of milk and the wooden box poised precariously at the junction of the upright and the slanting stick.

"A figure-four trap, eh?" queried the chief. "What do you expect to catch?"

"A mixture of a ghost and the figure of Justice," was Preston's enigmatic reply. "Come on--we'll lock the door and return later to see if the trap has sprung. Meanwhile, I'll send some wires to Sacramento, San Francisco, and other points throughout the state."

The telegram, of which he gave a copy to the local chief of police, "in order to save the expense of sending it," read:

Wire immediately if you know anything of recent arrival from Africa--probably American or English--who landed within past three days. Wanted in connection with Montgomery murder.

The message to San Francisco ended with the phrase "Watch outgoing boats closely," and that to Sacramento "Was in your city yesterday."

Hardly an hour later the phone rang and a voice from police headquarters in Sacramento asked to speak to "Postal Inspector Preston."

"Just got your wire," said the voice, "and I think we've got your man.

Picked him up on the street last night, unconscious. Hospital people say he's suffering from poisoning of some kind and don't expect him to live.

Keeps raving about diamonds and some one he calls 'Marsh.' Papers on him show he came into San Francisco two days ago on the _Manu_. Won't tell his name, but has mentioned Cape Town several times."

"Right!" cried Preston. "Watch him carefully until I get there. I'll make the first train out."

That afternoon Preston, accompanied by two chiefs of police, made his way into a little room off the public ward in the hospital in Sacramento. In bed, his face drawn and haggard until the skin seemed like parchment stretched tightly over his cheekbones, lay a man at the point of death--a man who was only kept alive, according to the physicians, by some almost superhuman effort of the will.

"It's certain that he's been poisoned," said the doctor in charge of the case, "but he won't tell us how. Just lies there and glares and demands a copy of the latest newspaper. Every now and then he drifts off into delirium, but just when we think he's on the point of death he recovers."

Motioning to the others to keep in the background, Preston made his way to the bedside of the dying man. Then, bending forward, he said, very clearly and distinctly: "Marshall Montgomery is dead!"

Into the eyes of the other man there sprang a look of concentrated hatred that was almost tangible--a glare that turned, a moment later, into supreme relief.

"Thank G.o.d!" he muttered. "Now I'm ready to die!"

"Tell me," said Preston, quietly--"tell me what made you do it."

"He did!" gasped the man on the bed. "He and his d.a.m.ned brutality. When I knew him his name was Marsh. We dug for diamonds together in South Africa--found them, too--enough to make us both rich for life. But our water was running low--barely enough for one of us. He, the skunk, hit me over the head and left me to die--taking the water and the stones with him."

He paused a moment, his breath rattling in his throat, and then continued:

"It took me five years to find him--but you say he's dead? You're not lying?"

Preston shook his head slowly and the man on the bed settled back and closed his eyes, content.

"Ask him," insisted the chief of police, "how he killed Montgomery?"

In a whisper that was barely audible came the words: "Sheep-stinger. Got me first." Then his jaws clicked and there was the unmistakable gurgle which meant that the end had come.

"Didn't he say 'sheep-stinger'?" asked the chief of police, after the doctor had stated that the patient had slipped away from the hands of the law.

"That's what it sounded like to me," replied Preston. "But suppose we go back to Montgomery's room and see what our ghost trap has caught. I told you I expected to land a figure of Justice--and if ever a man deserved to be killed it appears to have been this same Montgomery Marshall, or Marsh, as this man knew him."

The instant they entered the room it was apparent that the trap had sprung, the heavy box falling forward and completely covering the saucer of milk and whatever had disturbed the carefully balanced sticks.

Warning the chief to be careful, Preston secured a poker from an adjoining room, covered the box with his automatic, and then carefully lifted the box, using the poker as a lever.

A second later he brought the head of the poker down on something that writhed and twisted and then lay still, blending in with the pattern of the carpet in such a manner as to be almost invisible.

"A snake!" cried the chief. "But such a tiny one! Do you mean to say that its bite is sufficiently poisonous to kill a man?"

"Not only one, but two," Preston declared, "as you've seen for yourself.

See that black mark, like an inverted V, upon the head? That's characteristic of the cobra family, and this specimen--common to the veldts of South Africa where he is known as the 'sheep stinger'--is first cousin to the big king cobras. Montgomery's former partner evidently brought him over from Africa with this idea in mind. But when he was packing him in the box--the airhole in the end of it gave me the first inkling, by the way--he got careless and the snake bit him. Only medical attention saved his life until this afternoon, else he'd have pa.s.sed along before Montgomery. I think that closes the case, Chief, and in spite of the fact that the mails were used for a distinctly illegal purpose, I believe your department ought to handle the matter--not mine."

"But the trap--the milk? How'd you happen to hit on that?"

"When you told me what the special-delivery man said about the contents of the package 'wabbling' I figured that the box must have contained a snake," explained the Postal operative. "An animal would have made some noise, while a snake, if well fed, will lie silent for hours at a time.

The constant motion, however, would have made it irritable--so that it struck the moment Montgomery removed the lid of the box. That explains the wound in his hand. He knew his danger and deliberately fired, hoping to cauterize the wound and drive out the poison. It was too quick for him, though, or possibly the shock stunned him so that he fell.

"Then, in spite of the fact that your men claimed to have searched the room thoroughly, that noise in the corner warned me that whatever killed Montgomery was still here. Going on the theory that the majority of snakes are fond of milk, I rigged up the trap. And there you are!"

"Yes," concluded Quinn, "the majority of the cases handled by government detectives have to do with counterfeiting or smuggling or other crimes against the federal law--offenses which ought to be exciting but which are generally dull and prosaic. Every now and then, though, they stumble across a real honest-to-goodness thrill, a story that's worth the telling.

"I've got to be away for the next couple of months or so, but drop around when I get back and I'll see if I can't recall some more of the problems that have been solved by one of the greatest, though least known, detective agencies on the face of the earth."

THE END