"it beats anything i ever heard of—i can hardly believe it. sure you're not joking?"

"amazing—that's the word! i wonder what their game is now. h'm, i'm utterly befogged, or whatever you choose to call it."

"haven't we been easy marks, though?"

"now we are certain that mr. wingate and nat have been working some kind of a game on us."

the five ramblers had gathered in bob somers' room, and were discussing the astonishing turn in affairs with much animation.

"the whole thing must have been started on the very day that mr. wingate came down to look at the 'rambler.' probably he only gave nat a boat so that he could follow us."

"there's a lot of things we have to find out," observed dick; "who damaged the engine, for one."

"yes—and who blew up the 'rambler.'"

"and who took the 'nimrod.'"

"and—and—say, fellows, this everlasting mystery is positively getting on my nerves," said dick. "can't we do something to clear it up?"

"we must."

"one sure thing," replied bob, "they don't want us to continue our trip."

the five boys were so interested in their discussion that the afternoon slipped away almost before they knew it.

a light, quick step outside suddenly brought all conversation on the subject to an end. another instant, and nat entered the room.

"hello, where have you been for such a long time?" asked bob, carelessly.

"for one thing, took in a lot of moving picture shows," replied nat, without hesitation. "didn't expect to find you fellows here until about grub time, anyway."

"come on, fellows," put in dave; "that reminds me. a nice piece of roast and some mashed potatoes would go pretty well just now."

they all trooped down-stairs into the dining-room.

"what are we going to do after supper?" inquired tom clifton.

"oh, walk around and see what's going on."

"wish a fire or something else would happen," observed nat, charitably. "say, somers, how long are you going to stay in this place?"

"about two or three days."

"h'm—hang it all, we ought to put in at least a week, eh, chubby?"

bob smiled, as he led the way out into the street.

"well, nat," he asked, "haven't you any news for us?"

wingate began to laugh.

"yes!" he answered, pulling a letter out of his pocket. "listen to this, and you'll hear the funniest roast you ever came across."

he went off into another burst of merriment.

"hit your funny-bone, wingate?" asked dick travers.

"it's a letter from uncle parsons. christopher! but he has handed out a few choice remarks about poor old hacky. listen."

nat began to read.

"'when john hackett learned of your disobedient and disgraceful conduct, and my firm resolve to take them all back to kingswood, he acted in a fashion which i can hardly describe. his loud and impudent remarks encouraged the others. they actually defied me, made a rumpus in the hotel, then stamped out into the street, as if they were a lot of rowdies. not one of them has since put in an appearance. i consider john hackett the most impudent boy i ever came across, and i hope it is not your custom to be guided by anything he may say.'

"a fine, hot roast for poor old 'hatchet,'" gurgled nat. "uncle parsons is certainly sore. ha, ha! the whole crowd left him in the lurch."

next morning, just after breakfast, bob declared his intention of going to the post-office.

the members of the rambler club, accompanied by nat wingate, left the hotel in a body and were soon in the busiest section of the city.

"where is nat?" cried dick travers, a few moments later.

"that's so—what has become of him?" added dave.

nat was nowhere to be seen.

"he has given us the slip."

"is he up to some new trick?"

"boys!" exclaimed bob somers, suddenly, "i'm going to leave you."

"hold on i where are you bound?"

"to the house behind the picket fence. it may be a waste of time—but—"

"let us go along, too?" urged sam.

bob shook his head.

"too risky, sam."

"but i went the other day."

"that was different. can't wait to talk, fellows—see you later."

"perhaps nat has gone to meet his uncle and their mysterious friend," thought the boy. "i wish i could get a good look at that fellow's face."

at the next corner, he jumped on board a car, rode for some distance, then transferred to another line. when he got off, although still at some distance from his destination, he began to keep a sharp lookout for nat.

"the trailer trailed," he chuckled; "nat isn't quite so smart as he thinks he is."

bob scarcely breathed easily until he was back of the bushes which had helped to conceal him on the day before. a number of people were near, and he found it difficult to avoid observation.

the minutes seemed to slip by very slowly. the sun grew hotter and hotter, and bob, wiping his perspiring face, began to think that his vigil would result in nothing.

"whew, but it is warm!" he murmured. "i can't stand this much longer. don't see a sign of life now. by jingo! that isn't a bad idea."

a sudden thought had entered his head.

"it's pretty risky," he muttered; "but i'll do it. i haven't come all this way for nothing."

bob took a careful view of the deserted street, then arose and walked boldly toward the house.

"perhaps it won't do any harm, even if they do see me," he thought; "anyway—here goes."

pulling his hat well over his eyes, he made a bee-line for the big sycamore which stood just inside the curb. it was the work of only a few moments to reach it, when, with considerable agility, bob drew himself up into a crotch, and screened by the thick foliage began to climb slowly upward.

the shade of the tree was grateful to bob, but, as the moments flew by, he began to feel that detective work was not the most pleasant in the world.

"i don't suppose—"

the half uttered words came to an abrupt stop.

a faint sound of voices from below reached his ears. then the front door was opened and two figures appeared on the steps. they were mr. wingate and nat.

bob scarcely dared to breathe, as they walked slowly toward the gate.

"don't bother me about it any more," mr. wingate was saying; "this is only a matter of business, and we prefer to discuss it in private."

"i don't believe you've told me the real thing," growled nat. "why do you want to keep anything back?"

"you should not have been so silly as to leave the boys and come here. you ran away at clair bay, and now when i ask you to stay with your friends you come here to bother me with annoying questions."

"but why are you so afraid to answer them?" demanded nat.

"i declare! you would try the patience of a saint," cried mr. wingate, angrily. then he added, in a milder tone: "now, nat, if everything goes well, my promise is to be fulfilled. run along—i am keeping those gentlemen waiting."

nat was clearly in a disgusted frame of mind as he slowly walked away.

bob somers straightened up to ease his aching back. the expression on his face indicated the greatest astonishment.

"crickets, i'm glad to know this," he muttered. "nat wingate isn't half as bad as we thought. he did run away from his uncle, after all. what a piece of luck! guess even chubby will open his eyes when he hears the news."

in his cramped quarters, he had shifted from one position to another until it seemed as if every muscle was aching, but he kept to his post.

at length, after what seemed to be a very long wait, voices at the door again made him keenly alert.

four figures appeared.

gently pushing aside a branch, he was able to get a good view of the group. one was tall and slim, dressed in a gray suit and wore a straw hat.

but bob's glance quickly left this man to centre on two figures who had a strangely familiar look.

"where can i have seen them before?" he mused.

his eyes eagerly roved from one to the other, as the group approached the gate.

one of them presently turned. his profile was sharply outlined against the sunlit ground.

like a flash, bob recalled where he had seen the two before. it was on the little steamboat which they had encountered when passing through the lock.