“s-s—h!”

bob, who was a few feet in advance of his brother, held up his hand as a signal for him to stop. it was about three o’clock in the afternoon and they had been pushing their way through the thick forest for several hours. it had been hard traveling as the underbrush was dense and several times it had taken them a half hour or more before they could locate the stones which marked the boundary line between the united states and canada.

“what’s the matter?” jack whispered as he advanced cautiously to meet his brother.

“there’s a small cabin about three rods ahead of us and i think someone is in it. listen.”

the sound of a man’s voice came to them but he was speaking french and speaking it so rapidly that, although they strained their ears for some moments, they were unable to catch more than a word now and then.

“i think there’s three of them there,” jack whispered as he crept forward a few feet to where he could catch a glimpse of the cabin.

he stole softly back a few minutes later and bob knew, from the look on his face, that he was very much excited.

“that cabin is exactly like the one i saw up at moosehead,” he whispered as soon as he was beside bob. “and what’s more one of the men is the fellow who was in that other cabin. i mean the man who spoke to me while i was fishing. he came to the door while i was watching and looked around.”

“are you sure?”

“absolutely.”

“well i don’t know that there’s anything so strange about the cabin looking the same as the other one, the one that vanished. they build them very much alike up here.”

“i know they do, but—”

“but what?”

“nothing. i was just wondering.”

“well, i wish you’d do your wondering out loud. here’s a time when two heads are better than one.”

“i was just wondering how they happened to build two of them so exactly alike. but what had we better do now?”

“i think we’d better watch right here for awhile,” bob replied after a moment’s thought.

“my idea exactly, but don’t you think it would be a good plan to make a detour round in front and see if we can find any signs of a trail? that cabin must be pretty near on the line.”

“good idea,” bob agreed. “but we must be mighty careful.”

they at once struck off through the woods moving cautiously and keeping a good distance away from the cabin. it took them nearly an hour to reach the opposite side of it and they were obliged to confess that they had not seen anything that even remotely resembled a trail.

“well, i guess we’re on a cold scent,” bob declared as he stopped and wiped the perspiration from his face.

“looks like it,” jack agreed. “but what i can’t understand is why anyone should want to build a cabin away off here in the wilderness.”

“if we knew that we might know a whole lot and then again we might not know a thing more than we do now. but i move that we camp right here for the night at least and keep an eye on them. what do you think?”

“suits me. i’ve tramped about far enough anyhow,” and jack slipped his pack from his back.

they found a good place where they had a view of the cabin without danger of being seen and there they lay and watched until it began to get dusky in the forest. but they saw no one in all that time.

“they’re keeping mighty close whoever they are,” jack said.

“they sure are, but how about supper? i’m getting pretty lank.”

“you said a mouthful then and i second the motion. let’s go back to where we crossed that little brook. i guess the water will be fairly cold.”

the boys were obliged to eat a cold supper as they were afraid to make a fire for fear that the smoke would be seen by the inmates of the cabin.

“now i don’t think that we had both better go to sleep at the same time,” bob said a little later after had returned to their former place. “one of us had better keep watch. it would be mighty inconvenient to have one of those fellows stumble over us while we were asleep.”

“all right. you roll up in your blanket and i’ll take the first watch. no use for both of us to stay awake.”

bob tried to persuade jack to let him take the first watch but he would not listen to it declaring that he was not a bit sleepy and would not go to sleep even if he tried. so finally he gave in and was soon fast asleep on a bed of leaves a few feet back from where jack was stationed.

for some time a light showed in the cabin and once or twice the sound of voices came to the boy’s ears. but about ten o’clock the light went out and except for the soft murmur of the tree tops in the light breeze and the occasional hoot of an owl, all was still. there was no moon and jack could hardly see his hand before his face.

slowly the time passed. he began to grow sleepy and by eleven o’clock he was having all he could do to keep awake. swarms of mosquitoes hovered about him but they had had the foresight to bring along a bottle of citronella and they bothered him but little.

“they’d eat a fellow alive if it wasn’t for this stuff,” he thought as he got to his feet and moved about.

bob had made him promise that he would call him at twelve o’clock sharp. so, although he hated to disturb his brother, who was sleeping soundly, he gave him a slight shake at the appointed time.

“twelve o’clock and all’s well,” he whispered as bob sat up.

“anything happened?”

“not a thing. i believe we might as well go to sleep. i don’t believe anything will happen.”

“better be careful than sorry you know. i’ve had sleep enough. you go to it and i’ll keep an eye open.”

but in this bob was mistaken. he had had just sleep enough to make it practically impossible for him to keep awake. he struggled against the desire for an hour or more and then succumbed. dawn was breaking through the trees when he awoke. for a moment he wondered where he was and then as memory returned he started up with an exclamation of disgust.

“i’m a good one to keep watch,” he told himself. “if jack finds it out he’ll kid the life out of me and serve me right too,” he added as he leaned back against the tree.

it was still too dark to see more than a few feet and he waited until the shadows lifted and it was nearly daylight. then he parted a bush and looked toward the cabin. he rubbed his eyes and looked again. then he got slowly to his feet and stepped around in front of the bush. the cabin should now be plainly visible but nothing in the shape of a cabin greeted his vision.

“wonder if i’m seeing things,” he muttered. “i mean i wonder if i’m not seeing things that i ought to see,” he added.

he moved a little nearer to where the cabin had stood and finally, as nearly as he could judge, he was standing on the exact spot which it had occupied. not only had the cabin vanished into thin air but he could not find the slightest trace to indicate that a cabin had ever been there.

“it’s too many for me,” he muttered as he slowly made his way back to where jack was sleeping.

the boy was sleeping so soundly that bob was loath to disturb him, so he made his way to the little stream where he drank and washed his face.

“perhaps i’ll be able to see better now that i’ve got some of the sleep washed out,” he muttered as he started back again.

but if he had hoped that the cabin would put in a reappearance he was doomed to disappointment for there was no cabin there.

“the trouble wasn’t with my eyes anyway,” he thought as he again retraced his steps.

jack was awake when he returned.

“well, how’s tricks?” he greeted him.

“tricks is about right,” bob said as he took his brother by the arm. “come with me. i want to show you something.”

he led the way without another word until they reached the place where the cabin could be seen had it been there.

“now take a look and tell me if there’s a cabin there.”

jack looked and for a moment was silent, then he turned to bob.

“mebby you’ll believe what i told you about that other cabin now,” he grinned.

“but what does it mean?”

“it’s mean enough for most anything,” jack replied. “it’s a case of now you see it and now you don’t.”

“with the emphasis on the don’t.”

“and you didn’t hear a thing?”

bob’s face turned red.

“i guess i might as well fess up,” he said. “the fact is i went to sleep at the switch so to speak. i don’t know how it happened but i was sitting there with my back against a tree and the first thing i knew i didn’t know anything. when i woke up it was morning. i’m mighty sorry, but—”

“no apologies are necessary,” jack interrupted. “i came mighty near to doing the same thing and it probably wouldn’t have made a bit of difference if you had kept awake. i fancy the old cabin would have vanished just the same.”

“that’s not the point. it’s certainly got me worried to think that i couldn’t keep awake. suppose i’d been on a post in time of war and—”

“and suppose the cow had jumped over the moon,” jack interrupted. “if anything had depended on it you’d have kept awake fast enough. but, bob, this thing has got me dippy. this is the twentieth century and log cabins aren’t in the habit of vanishing into thin air. if this was back in fairy times it wouldn’t be surprising but now, well, all i got to say is that it’s got me bughouse.”

“bughouse is right,” bob agreed, a serious look on his face. “but what’s the answer?”

“guess we’ll have to wait till we get more data, as professor sharp used to say, before we can answer that question.”

for more than an hour the two boys searched the immediate vicinity hoping to obtain some clue to the mystery. but their search was all in vain. so far as they were able to discover no one had ever been there before and finally they were obliged to give it up.

“well, anyhow, i guess we’ll be able to build a fire and have a hot breakfast,” bob declared as they slowly made their way back to where they had left their packs.

“i have an idea that there may be trout in that brook,” jack suggested.

“suppose you build a fire and get the coffee going while i have a try at it.”

jack’s idea proved a good one for by the time bob had the coffee boiling he was back with a dozen speckled beauties averaging about a half a pound. the fish proved a welcome addition to their larder and by the time breakfast was over they were both in better spirits.

“nothing is so bad but what it might be worse,” bob said as he finished rolling his pack.

“i suppose we might as well keep along the border,” jack suggested.

“i don’t know of anything better.”

“even if we find nothing more exciting than log cabins which vanish while you wait,” jack laughed.

they were about to start when a slight sound a little to their right caught bob’s ear.

“somebody or something is coming this way,” he whispered holding up his hand for silence.

“mebby it’s that log cabin,” jack chuckled.

“let’s get back in those bushes and hide. it may be someone we wouldn’t care to see.”

they quickly hid themselves in the thick brush and waited with bated breath.

soon they could plainly hear something making its way toward them and it was evident that, whatever it was, it would pass close to them. in a moment or two the sound of voices came to them and bob whispered.

“that sounds very much like pierre to me.”

his fears were almost immediately realized for, as he carefully parted the bushes in front of his face, he caught sight of the big frenchman. with him were two other men, both strangers to bob but jack at once recognized one of them as the man he had seen twice at the door of the vanishing cabin.

the men stopped short as they caught sight of the smouldering fire.

“they were here only a little while ago,” pierre declared, speaking in french. “they can’t be far off and we’ll soon have them.”

bob nudged jack with his elbow as a warning for him to keep perfectly quiet in the hope that the men would fail to locate them. but his hope was quickly dashed to the ground. big pierre, as though led by a scent, came straight toward them and in another minute had parted the brush and was looking directly into bob’s eyes. but he quickly saw that he was looking into something else as well, for bob had him covered with a small but business-like looking automatic.

“were you looking for us?” bob asked pleasantly as he got to his feet.

for a moment the man hesitated as though at a loss what to say.

“non. we look for beeg man,” he finally managed to say.

“well, i’m glad that it wasn’t we who were putting you to all the trouble. but you made a pretty quick trip to skowhegan.”

“i no gone dar yet. mebby go ver’ queek now.”

“i see. well as long as you were not looking for us we might as well be moving i guess.”

jack had also drawn his revolver and was holding it in his hand although not pointing it at any of the men. they slowly backed away, bob still keeping pierre covered.

“we’ll have to look sharp, jack,” he said in a low tone. “those fellows mean trouble and they may follow us. just as soon as we get out of sight we’ll slip behind a couple of trees and see what they’re up to.”

as long as they were in sight the three men stood still making no motion either to follow them or to go away.

“now you get behind that tree and i’ll take this one,” bob said as soon as he was sure that they were out of sight.

they waited for fully fifteen minutes but there was no sign of pursuit.

“i guess they aren’t going to follow us after all,” bob whispered as he stepped from behind the tree and retraced his steps a short distance.

“they seem to have gone,” he announced coming back a moment later. “i guess the guns were too many for them.”

“for the time being, perhaps, but something tells me that we haven’t seen the last of them yet.”

“i’m afraid you’re right there and we’ll keep a mighty sharp watch.” bob agreed as he led the way through the woods.

they made no effort to make time. they were far more desirous of making a thorough search as they went along and not to miss anything which might furnish a clue. shortly after twelve o’clock they stopped to eat their dinner by the side of a little stream.

they had finished and were about to start again when suddenly the stillness of the forest was broken by the call of the loon.

“listen,” bob said as he grabbed jack’s arm. “you’ll hear an owl hoot in a minute.”

his prediction was made good almost immediately.

“that may be a real owl,” jack declared as the last hoot boomed through the forest, “but if a loon should hear that punk imitation he’d bury his head beneath the waves for shame.”

“just what i thought the other night and, knowing that the loon call is a fake we can be pretty certain that the owl belongs to the same species and anyhow, it’s the same ‘loon’ that i heard the other time.”

“i guess that makes it pretty certain that it is a signal.”

“no doubt about that and i think it also means that the trail is getting fairly warm.”

“if only we had not run up against them,” jack sighed as he leaned back against a friendly spruce.

“i know,” bob sympathized, “but what can’t be cured must be endured, you know.”

by four o’clock they had covered some five miles from where they had eaten their dinner. three times during the afternoon they had heard the signal repeated. for the past two hours bob had experienced a feeling that they were being followed. several times, on turning his head, he had fancied that a bush had moved and once he was almost sure that he had caught a glimpse of a form as it dodged behind a tree some distance off to the right. he had said nothing to his brother as yet, but now, as they sat down for a short rest at the foot of a tall pine, he said:

“jack, i’m pretty certain that we’re being shadowed.”

“i know it. that is i’ve thought so for an hour but didn’t say anything for fear you’d say i was seeing things again.”

“no danger of that,” bob laughed. “not after seeing that cabin or whatever it was. i’ll never accuse you of ‘seeing things’ again. you can bet your bottom dollar on that.”

so far they had seen no evidence of a trail or road leading over the border.

“they must take the stuff across either through the air or else through an underground passage,” jack declared.

“of course either one is possible especially the former but, you remember, the captain said that no air ship had been seen up here for some months, so it’s not very likely.”

“well, of course that’s right but i move that we camp for the night pretty soon. to tell the truth i’m rather tired.”

“second the motion just as soon as we come to a spring or a brook.”

fortunately they were not long in finding an ideal place for a camp within a quarter of a mile and jack declared that he had never seen a more likely brook for trout. and within an hour he had proved his judgment by returning with a full dozen of the largest brook trout bob had ever seen.

“it’s too bad,” bob said a little later as they were washing up their supper dishes by the side of the brook, “but we’ll have to stand watch to-night. it wouldn’t be safe for both of us to go to sleep at the same time.”

jack readily agreed with him and insisted that he would take the first watch but to this bob would not hear, declaring that he was not tired and that he knew the other was. after some argument jack yielded after he had made bob promise that he would call him promptly on the stroke of twelve.

“i’ll have to be careful not to go to sleep on watch this time,” bob thought as he leaned back against the tree.

jack had been asleep for nearly two hours and not a sound save the call of an occasional night bird and the distant croaking of a colony of frogs had disturbed the silence of the deep forest.

“two hours more,” he thought as he glanced at his watch. “and i’m having to fight to keep awake now. guess i’d better move about a bit.”

he got slowly to his feet and was about to move toward the brook with the intention of plunging his head into the cold water, when a slight sound off to his left caught his ear. a dead branch cracked as if some man or beast had stepped on it.

he strained his ears for several minutes but the sound was not repeated.

“probably a deer,” he thought as he groped his way toward the little stream.

he had just ducked his face in the water for the second time when he again heard a stick crack. this time it was much nearer. he drew his automatic from his pocket and listened. almost immediately the sound was repeated.

“that’s no deer,” he muttered as he moved noiselessly to the right.

automatic in one hand and his flash light in the other he groped his way between the thick trees moving as rapidly as he dared. his idea was to approach the intruder from the side instead of in the direction in which he was moving. in this way he figured that he would stand a better chance of finding out who it was and remain undiscovered himself.

stopping every few minutes to listen he could hear some heavy object moving through the underbrush a short distance to his left.

“he evidently is in no hurry,” he thought as he changed his course slightly toward the sound.

“i believe he’s getting farther away,” he thought a few moments later as he paused to listen. “mebby it was only a deer after all.”

two or three times more he heard the cracking but as it was farther away each time he soon decided to make his way back to camp feeling convinced that it was only some wild animal.

it was nearly eleven o’clock by the time he was back.

“well, it killed an hour anyhow,” he thought as he once more sat down at the foot of the big pine.

he was no longer sleepy as the cold water had washed the drowsiness from his eyes. but the time passed very slowly and it seemed to the boy that it must be nearly morning when at last his watch told him that it was time to call his brother.

“i wouldn’t do it if he hadn’t made me promise,” he thought as he rose and went slowly toward the big spruce a few feet to his left where jack had rolled himself in a blanket.

“it’s a shame to wake him,” he thought, but a moment later he was standing as if spellbound for there was no jack there to waken.