"what's de mattah? shall i come in? am anybody hurted?" yelled eradicate sampson as he pounded on the rear door of the aeroplane shed. "let me in, massa tom!"

"all right! wait a minute! i'm coming!" called mr. jackson. he tried to peer through the darkness, to where a huddled heap indicated the presence of tom. then he thought of the electric lights, which were run by a storage battery when the dynamo was shut down, and a moment later the engineer had switched on the incandescents, filling the big shed with radiance.

"tom, are you badly hurt?" gasped mr. jackson.

there was no answer, for tom was unconscious.

"let me in! let me git at dat robber wif mah club!" cried the colored man eagerly.

knowing that he would need help in carrying tom to the house, mr. jackson hurried to the back door. he had a key to it, and it was quicker to open it than to send eradicate away around the shed to the front portals.

"whar am he?" gasped the faithful darky, as he took a firmer grasp of his club and looked around the place. "let me git mah hands on him! i'll feed him t' boomerang, when i gits froo wif him!"

"he's gone," said the engineer. "help me look after tom. i'm afraid he's badly hurt."

they hastened to the unconscious lad. on one side of his head was a bad cut, which was bleeding freely.

"oh! he's daid! i know he's daid!" wailed eradicate.

"not a bit of it. he isn't dead, but he may die, if we don't get him into the house, and have a doctor here soon," said mr. jackson sternly. "catch hold of him, rad, and, mind, don't carry on, and get excited, and scare mr. swift. just pretend it isn't very bad, or we'll have two patients on our hands instead of only tom."

they managed to get the youth into the house, and, contrary to their fears, mr. swift was not nearly so nervous as they had expected. calmly he took charge of matters, and even telephoned for dr. gladby himself, while mr. jackson and eradicate undressed tom and got him to bed. mrs. baggert busied herself heating water and getting things in readiness for the doctor, who had promised to come at once.

tom was just regaining consciousness when the physician came in, having driven over at top speed.

"what—what happened? did the humming-bird fall?" asked tom in a whisper, putting his hand to his head.

"no, something fell on you, i guess," said the doctor, who had been hurriedly told of the circumstances. "but don't worry, tom. you'll be all right in a few days. you got a bad cut on the head, but the skull isn't fractured, i'm glad to say. here, now, just drink this," and he gave tom some medicine he had mixed in a glass.

the cut was soon dressed, and tom felt much better, though weak and a trifle dizzy.

"did he hit me with the hatchet?" he asked mr. jackson.

"i couldn't tell," was the engineer's reply, "it all happened so quickly. in another instant i'd have bowled him over, instead of him landing on you, but i just missed him. he either used the hatchet, or some blunt instrument."

"well, don't talk about it now," urged the doctor. "i want tom to get quiet and go to sleep. he'll be much better in the morning, but i must forbid any aeroplane flights." and he shook his finger at tom in warning. "you'll have to lie quiet for several days," he added.

"all right," agreed the young inventor weakly, and then he dozed off, for the physician had given him a quieting medicine.

"haven't you any idea who it was?" asked dr. gladby of mr. jackson, as he prepared to leave.

"not the slightest. it was no one tom or i had ever seen before. but whoever it was, he intended to destroy the humming-bird, that was evident!"

"the scoundrel! i'm glad you foiled him in time; but it's too bad about tom. however, we'll soon have him all right again."

"i knows who done it!" broke in eradicate, who was a sort of privileged character about the swift home.

"who?" asked mr. jackson.

"it were dat andy foger. leastways, he send dat man heah t' make mincemeat oh de hummin'-bird. i's positib 'bout dat, so i am!" and eradicate grinned triumphantly.

"well, perhaps andy did have a hand in it," admitted mr. swift, "but we have no proof of it, i can't see what his object would be in wanting to destroy tom's new craft."

"pure meanness. afraid that tom will beat him in the race," suggested mr. jackson.

"it's too big a risk to take," went on the aged inventor. "i'm inclined to think it might be one of the gang of men who made the diamonds in the cave in the mountains. they might have sent a spy on east, and he might try to damage the aeroplane to be revenged for what tom and mr. jenks did to them."

"it's possible," agreed the engineer. "well, we'll wait until tom can talk, and we'll go over it with him."

"not until he is stronger, though," stipulated the physician as he went away. "don't excite tom for a few days."

the young inventor was much better the following day, and when dr. gladby called he said tom could sit up for a little while. two days later tom was well enough to be talked to, and his father and mr. jackson went over all the details of the matter. mr. damon, who had returned home, came to see his friend as soon as he heard of his plight, and was also a member of the consulting party.

"bless my dictionary!" exclaimed the eccentric man. "i wish i had been here to take a hand in it. but, tom, do you believe it was one of the diamond-making gang?"

"i hardly think so," was the reply. "they would take some other means of revenge than by destroying my new aeroplane. i'm inclined to think it was some one who is in with andy foger."

"then we'll hire detectives, and locate him and them," declared mr. damon, blessing several things in succession.

tom, however, did not like that plan, and it was decided to do nothing right away. in another few days tom was able to be up, though he was still a semi-invalid, not venturing out of the house.

it was one afternoon, when, rather tired of his confinement, he was wishing he could resume work on his air craft, that mrs. baggert came in, and said:

"some one to see you, tom."

"is it mr. damon?"

"no, it's a lady. she—"

"oh, tom! how are you?" cried a girlish voice, and mary nestor walked into the room, holding out both hands to the young inventor. tom, with a blush, arose hastily.

"no! no! sit still!" commanded the girl. "oh! i'm so sorry to hear about your accident! in fact, i only heard this morning. we've been away, mamma and i, and we just got back. tell me all about it, that is, if you feel able. but don't exert yourself. oh! i wish i had hold of that man!"

and miss nestor clenched her two pretty little hands and set her white, even teeth grimly together, as though she would do most desperate things indeed.

"i wish you did, too!" exclaimed tom. "that is, so you could hold him until i had a chance at him. but i'm all right now. it was very good of you to call. how are you, and how are your folks?"

"very well. but i came to hear about you. tell me," and she looked anxiously at tom, while mrs. baggert discreetly withdrew to the adjoining room, and made a great noise, rattling papers and moving chairs about.

thereupon tom told what had happened, while mary nestor listened interestedly and with expressions of fear at times.

"but if andy had anything to do with it," concluded tom, "i can't understand what his object is. andy is acting very strangely lately. we can't locate him, nor find out where he is building his airship. that's what i want to know; but mr. damon and i, after a lot of trouble, only found his aeroplane shed empty."

"and you want to find out where andy foger is building his aeroplane which he has entered in the big race?" asked miss nestor.

"that's what i'd like to know," declared tom earnestly. "only we can't seem to do it. no one knows."

"why don't you write to mr. sharp, or some one of the aviation meet committee?" asked the girl simply. "they would know, for you say andy made his formal entry with them, and the rules require him to tell from what city and state he will enter his craft. write to the committee, tom."

for a moment the young inventor stared at her. then he banged his fist down on the arm of his chair.

"by jove, mary! that's the very thing!" he cried. "i wonder why i never thought of that, instead of fiddling around in disguises, and things like that? i wonder why i never thought of that plan?"

"perhaps because it was so simple," she answered, with a pretty blush.

"i guess that's it," agreed tom. "it takes a woman to jump across a bridge to a conclusion every time. i'll write to mr. sharp at once."