out of the cabin of the now stationary airship hurried the three travelers; out into the pelting rain, which was lashed into their faces by the strong wind. tom was the first to emerge.

"we're on something solid!" he cried, stamping his feet. "a rock, i guess."

"gracious, i hope we're not on a rock in the midst of a river!" exclaimed mr. damon. "bless my soul, though! the water does seem to be running around my ankles."

"there's enough rain to make water run almost up to our necks," called mr. sharp, above the noise of the storm. "tom, can you make out where we are?"

"not exactly. is the ship all right?"

"i can't see very well, but there appears to be a hole in the gas container. a big one, too, or we wouldn't have fallen so quickly."

the plight of the travelers of the air was anything but enviable. they were wet through, for it needed only a few minutes exposure to the pelting storm to bring this about. they could not tell, in the midst of the darkness, where they were, and they almost feared to move for fear they might be on top of some rock or precipice, over which they might tumble if they took a false step.

"let's get back inside the ship," proposed mr. damon. "it's warm and dry there, at all events. bless my umbrella, i don't know when i've been so wet!"

"i'm not going in until i find out where we are," declared tom. "wait a minute, and i'll go in and get an electric flash lantern. that will show us," for the lightning had ceased with the great crash that seemed to have wrecked the red cloud. the rain still kept up, however, and there was a distant muttering of thunder, while it was so black that had not the lights in the cabin of the airship been faintly glowing they could hardly have found the craft had they moved ten feet away from it.

tom soon returned with the portable electric lamp, operated by dry batteries. he flashed it on the surface of where they were standing, and uttered an exclamation.

"we're on a roof!" he cried.

"a roof?" repeated mr. damon.

"yes; the roof of some large building, and what you thought was a river is the rain water running off it. see!"

the young inventor held the light down so his companions could observe the surface of that upon which the airship rested. there was no doubt of it. they were on top of a large building.

"if we're on a roof we must be in the midst of a city," objected mr. damon. "but i can't see any lights around, and we would see them if we were in a city, you know."

"maybe the storm put the lights out of business," suggested mr. sharp. "that often occurs."

"i know one way we can find out for certain," went on tom.

"how?"

"start up our search lamp, and play it all around. we can't make sure how large this roof is in the dark, and it's risky trying to trace the edges by walking around."

"yes, and it would be risky to start our searchlight going," objected mr. sharp. "people would see it, and there'd be a crowd up here in less than no time, storm or no storm. no, we've got to keep dark until i can see what's the matter. we must leave here before daylight."

"suppose we can't?" asked mr. damon. "the crowds will be sure to see us then, anyhow."

"i am pretty sure we can get away," was the opinion of the balloonist. "even if our gas container is so damaged that it will not sustain us, we are still an aeroplane, and this roof being flat will make a good place to start from. no, we can leave as soon as this storm lets up a little."

"then i'm going to have a look and find out what sort of a building this is," declared tom, and, while mr. sharp began a survey, as well as he could in the dark, of the airship, the young inventor proceeded cautiously to ascertain the extent of the roof.

the rain was not coming down quite so hard now, and tom found it easier to see. mr. damon, finding he could do nothing to help, went back into the cabin, blessing himself and his various possessions at the queer predicament in which they found themselves.

flashing his light every few seconds, tom walked on until he came to one edge of the roof. it was very large, as he could judge by the time it took him to traverse it. there was a low parapet at the edge. he peered over, and an expanse of dark wall met his eyes.

"must have come to one side," he reasoned. "i want to get to the front. then, maybe, i can see a sign that will tell me what i want to know."

the lad turned to the left, and, presently came to another parapet. it was higher, and ornamented with terra-cotta bricks. this, evidently, was the front. as tom peered over the edge of the little raised ledge, there flashed out below him hundreds of electric lights. the city illuminating plant was being repaired. then tom saw flashing below him one of those large signs made of incandescent lights. it was in front of the building, and as soon as our hero saw the words he knew where the airship had landed. for what he read, as he leaned over, was this:

middleville arcade

tom gave a cry.

"what's the matter?" called mr. sharp.

"i've discovered something," answered tom, hurrying up to his friend. "we're on top of the middleville arcade building."

"what does that mean?"

"it means that we're not so very far from home, and in the midst of a fairly large city. but it means more than that."

"what?" demanded the balloonist, struck by an air of excitement about the lad, for, as tom stood in the subdued glow of the lights from one of the airship's cabin windows, all the others having been darkened as the storm slackened, his, eyes shone brightly.

"this is the building where anson morse, one of the gang that robbed dad, once had an office," went on tom eagerly. "that was brought out at the trial. and it's the place where they used to do some of their conspiring. maybe some of the crowd are here now laying low."

"well, if they are, we don't want anything to do with that gang," said mr. sharp. "we can't arrest them. besides i've found out that our ship is all right, after all. we can proceed as soon as we like. there is only a small leak in the gas container. it was the generator machine that was put out of business by the lightning, and i've repaired it."

"i want to see if i can get any trace of the rascals. maybe i could learn something from the janitor of the arcade about them. the janitor is probably here."

"but why do you want to get any information about that gang?"

"because," answered tom, and, as mr. damon at that moment started to come from the cabin of the airship, the lad leaped forward and whispered the remainder of the sentence into the ear of the balloonist.

"you don't mean it!" exclaimed mr. sharp, in a tense whisper. tom nodded vigorously.

"but how can you enter the building?" asked the other. "you can't drop over the edge."

"down the scuttle," answered tom. "there must be one on the roof, for they have to come up here at times. we can force the lock, if necessary. i want to enter the building and see where morse had his office."

"all right. go ahead. i'll engage mr. damon here so he won't follow you. it will be great news for him. go ahead."

under pretense of wanting the help of the eccentric man in completing the repairs he had started, mr. sharp took mr. damon back into the cabin. tom, getting a big screwdriver from an outside toolbox, approached the scuttle on the roof. he could see it looming up in the semidarkness, a sort of box, covering a stairway that led down into the building. the door was locked, but tom forced it, and felt justified. a few minutes later, cautiously flashing his light, almost like a burglar he thought, he was prowling around the corridors of the office structure.

was it deserted? that was what he wanted to know. he knew the office morse had formerly occupied was two floors from the top. tom descended the staircase, trying to think up some excuse to offer, in case he met the watchman or janitor. but he encountered no one. as he reached the floor where he knew morse and his gang were wont to assemble, he paused and listened. at first he heard nothing, then, as the sound of the storm became less he fancied he heard the murmur of voices.

"suppose it should be some of them?" whispered tom.

he went forward, pausing at almost every other step to listen. the voices became louder. tom was now nearly at the office, where morse had once had his quarters. now he could see it, and his heart gave a great thump as he noticed that the place was lighted. the lad could read the name on the door. "industrial development company." that was the name of a fake concern headed by morse. as our hero looked he saw the shadows of two men thrown on the ground glass.

"some one's in there!" he whispered to himself. he could now hear the voices much plainer. they came from the room, but the lad could not distinguish them as belonging to any of the gang with whom he had come in contact, and who had escaped from jail.

the low murmur went on for several seconds.

the listener could make out no words. suddenly the low, even mumble was broken. some one cried out "there's got to be a divvy soon. there's no use letting morse hold that whole seventy-five thousand any longer. i'm going to get what's coming to me, or—"

"hush!" some one else cried. "be quiet!"

"no, i won't! i want my share. i've waited long enough. if i don't get what's coming to me inside of a week, i'll go to shagmon myself and make morse whack up. i helped on the job, and i want my money!"

"will you be quiet?" pleaded another, and, at that instant tom heard some one's hand on the knob. the door opened a crack, letting out a pencil of light. the men were evidently coming out. the young inventor did not wait to hear more. he had a clue now, and, running on tiptoes, he made his way to the staircase and out of the scuttle on the roof.