guesses," said Carl, shaking his head, "aber ve don'd know nodding. Dot roll oof bapers don'd pelong to Prady. Vell, oof dot's der gase, whose bapers vas dey?"

"That's a conundrum."

"Vill you dake dem py der bolice?"

"I've been thinking of that, and I believe I'll talk with Mr. Harkrider before I do anything more. He'll tell us just what to do, and I'm sure his advice will be good. You see, Carl, we're not entitled to the papers any more than Brady is, when you come to figure the thing down to a fine point. If the fellow who lost them out of the car turned up and claimed them, we'd have to give them to him."

Mr. Harkrider was superintendent for the Lestrange Manufacturing Company, the Eastern representatives of the Jarrot Automobile Company of St. Louis. Following the Borden cup race, in Kansas, Matt had entered the services of the Jarrot people, and they had sent him to Chicago to take part in the five-day race at the Coliseum. While waiting for the race to start, Matt and Carl had had the use of any machine they wanted in the Lestrange garage, so they had put in their time riding around the city and out into the suburbs. That is how they happened to be on the road beyond South Chicago at the time the Hawk was running away with the two aeronauts.

Unusual experiences always seemed to gravitate toward Matt, and this air-ship affair was one of the most novel that had ever come his way. What it was leading up to, he did not know, but it was evident there was a whole lot more to the matter than appeared on the surface.

After a quick and uneventful run into Chicago, Matt drove the automobile into the Lestrange garage and asked for Mr. Harkrider. To his disappointment, Mr. Harkrider had left for the day and would not return to the garage until the following morning.

"Well," said Matt, as he and Carl left the garage and proceeded toward their boarding house, "I guess the delay won't make much difference. I'll be busy with the race to-morrow, but you can take the papers, Carl, and do with them whatever Mr. Harkrider advises."

It was nearly supper time, and after the boys had had a wash, and a good meal, they went up to their room.

Close to eight o'clock, just as they were getting ready for bed, a rap fell on the door. Matt answered the summons and found a boy with a telegram.

The young motorist had been receiving a great many telegrams, since his Kansas victory, and supposed the message must be from some motor-car manufacturer who wanted to secure his services.

But he was destined to a surprise.

The telegram had been sent to the Lestrange garage, and by the foreman there forwarded to the boarding place.

"Matt King, Care Lestrange Company, Chicago:

"Come immediately to twenty-one-naught-nine Hoyne Street, South Chicago. Important matter relative to runaway air-ship. I will pay your expenses.

"Hamilton Jerrold."

"More aboudt dot air-ship pitzness," muttered Carl. "Who vas dot Jerrold feller?"

"He must be the man that Brady told us about," said Matt. "Jerrold seems to be a rival of Brady's, in this air-ship matter, and the message looks like a good clue. It won't do any harm to follow it up, anyhow."

"Dere iss somet'ing about dot vat I don'd like," demurred Carl. "I got some hunches dere iss underhandt vork afoot."

"I know there's underhand work going on," said Matt, "but we've been rung in on the deal and have got to see it through. I'm curious to learn more about the affair."

"Meppy dot same curiosidy vill make you some drouples," suggested Carl. "You can't haf dot, ven der racing iss on do-morrow."

"The Jarrot people have several good men in the five-day race, so it won't make much difference if I'm not one of the drivers. Anyhow, I don't intend to be all day in South Chicago."

"It don'd look righdt for you to go pack dere alone," grumbled Carl. "I vouldn't be easy a minid."

"I am not going alone," laughed Matt. "You're going along, Carl."

The Dutch boy brightened at once and had no more objections to offer.

"Ach, dot's tifferent! Ve vill shdart ad vonce. How ve go? On a pubble?"

"No, we'll take a railroad train. I don't want to go fooling with a car at this time of night."

"Is dere a train ve can ketch?"

"Lots of them. South Chicago is a suburb, and we can leave here every half hour. We ought to be back by midnight."

Without debating the matter further, the boys started forthwith.

CHAPTER V.

2109 HOYNE STREET.

Hoyne Street was easily found. A number of blast furnaces stood so near the house the two chums were looking for that the flames from their tall chimneys lighted up the surroundings so brilliantly that they were able to read the number over the door.

The house was a two-story frame structure. The gas and smoke from the neighboring iron mills had shriveled and scorched everything in that part of the town. Even by night, and under the glow of the furnaces, Hoyne Street had a dismal and dreary appearance.

No. 2109 was set well back from the sidewalk. Two branching wings, in front, made the house look like a deserted manufacturing plant. This impression was heightened by several broken windows.

There were no lights in the windows other than the reflected glare from the high chimneys.

"Whoosh!" muttered Carl, as he and Matt came close to the front of the house and read the number. "Dot's der blace, Matt, aber it don'd look pooty goot to me. Der feller vat lifs dere don'd got enough money, I bed you, to pay for sending dot delegram. Der hen oof drouple iss aboudt to hatch somet'ing."

"It may be," answered Matt, who likewise had a queer premonition of trouble, "but we've come this far and I'm going to see the thing through. If anything goes wrong in that house it will be on account of that roll of blue prints. I'll leave the roll with you, Carl, and you can stay outside. I won't be in the house more than fifteen minutes at most."

"Vell, you look a leedle oudt, Matt, dot's all. Oof somet'ing goes wrong mit you, led off a yell und I vill come gallywhooping."

"I don't think anything will go wrong with me if I haven't those papers in my pocket."

Carl shivered.

"Chee, but der leedle fires on der chimneys iss prighdt. Somet'ing aboudt dis blace gifs me a creepiness oof der skin. Be jeerful, be jeerful! Don'd shday in dere longer as den minids, Matt, oder I vas likely to t'row fits."

"I'll come out as soon as I can, Carl," answered Matt. "Don't fret. I'm able to take care of myself in a pinch."

"Oof you see der pinch fairst, yah, I bed you! Aber oof der pinch come ven you don'd vas looking, den vat?"

Matt laughed as he turned away, climbed a short flight of steps and drummed on the front door. He had to rap three or four times before his summons was answered.

A light showed itself through a fan-shaped transom over the door, and a hand could be heard fumbling with a rusty bolt. In a minute or so the door was drawn open and a girl stood revealed. She carried a lamp with a smoked chimney, and one of her slender hands protected the flame from the draft.

She was eighteen or nineteen years old, and, in spite of her coarse calico gown, she was extremely pretty. Her prettiness, however, was not what impressed Matt. The first thing he noticed was that the hand shielding the lamp was trembling. Lifting his eyes to the girl's face, he observed that she wore a frightened look.

"Does Mr. Jerrold live here?" Matt asked.

The girl stared at him; her lips moved, but no sound came through them. Matt repeated the question.

"Y-y-yes," faltered the girl.

"My name's King," answered Matt. "Mr. Jerrold sent me a telegram and asked me to come here to-night."

The girl leaned forward