mr. swift was lying on the floor, where he had fallen, in front of his bed, as he was preparing to retire. there was no mark of injury upon him, and at first, as he knelt down at his father's side, tom was at a loss to account for what had taken place.

"how did it happen? when was it?" he asked of mrs. baggert, as he held up his father's head, and noted that the aged man was breathing slightly.

"i don't know what happened, tom," answered the housekeeper, "but i heard him fall, and ran upstairs, only to find him lying there, just like that. then i called you. hadn't you better have a doctor?"

"yes; we'll need one at once. send eradicate. tell him to run—not to wait for his mule—boomerang is too slow. oh, no! the telephone, of course! why didn't i think of that at first? please telephone for dr. gladby, mrs. baggert. ask him to come as soon as possible, and then tell garret jackson to step here. i'll have him help me get father into bed."

the housekeeper hastened to the instrument, and was soon in communication with the physician, who promised to call at once. the engineer was summoned from another part of the house, and then eradicate was aroused.

mrs. baggert had the colored man help her get some kettles of hot water in readiness for possible use by the doctor. mr. jackson aided tom to lift mr. swift up on the bed, and they got off some of his clothes.

"i'll try to see if i can revive him with a little aromatic spirits of ammonia," decided tom, as he noticed that his father was still unconscious. he hastened to prepare the strong spirits, while he was conscious of a feeling of fear and alarm, mingled with sadness.

suppose his father should die? tom could not bear to think of that. he would be left all alone, and how much he would miss the companionship and comradeship of his father none but himself knew.

"oh! but i mustn't think he's going to die!" exclaimed the youth, as he mixed the medicine.

mr. swift feebly opened his eyes after tom and mr. jackson had succeeded in forcing some of the ammonia between his lips.

"where am i? what happened?" asked the aged inventor faintly.

"we don't know, exactly," spoke tom softly. "you are ill, father. i've sent for the doctor. he'll fix you up. he'll be here soon."

"yes, i'm—i'm ill," murmured the aged man. "something hurts me—here," and he put his hand over his heart.

tom felt a nameless sense of fear. he wished now that he had insisted on his parent consulting a physician some time before, when mr. swift first complained of a minor ailment. perhaps now it was too late.

"oh! when will that doctor come?" murmured tom impatiently.

mrs. baggert, who was nervously going in and out of the room, again went to the telephone.

"he's on his way," the housekeeper reported. "his wife said he just started out in his auto."

dr. gladby hurried into the room a little later, and cast a quick look at mr. swift, who had again lapsed into unconsciousness.

"do you think he—think he's going to die?" faltered tom. he was no longer the self-reliant young inventor. he could meet danger bravely when it threatened himself alone, but when his father was stricken he seemed to lose all courage.

"die? nonsense!" exclaimed the doctor heartily. "he's not dead yet, at all events, and while there's life there's hope. i'll soon have him out of this spell."

it was some little time, however, before mr. swift again opened his eyes, but he seemed to gain strength from the remedies which dr. gladby administered, and in about an hour the inventor could sit up.

"but you must be careful," cautioned the physician. "don't overdo yourself. i'll be in again in the morning, and now i'll leave you some medicine, to be taken every two hours."

"oh, i feel much better," said mr. swift, and his voice certainly seemed stronger. "i can't imagine what happened. i came upstairs, after tom had received a visit from the minister, and that's all i remember."

"the minister, father!" exclaimed tom, in great amazement. "the minister wasn't here this evening! that was mr. gunmore, the aviation secretary. don't you remember?"

"i don't remember any gentleman like that calling here to-night," mr. swift said blankly. "it was the minister, i'm sure, tom."

"the minister was here last night, mr. swift," said the housekeeper.

"was he? why, it seems like to-night. and i came upstairs after talking to him, and then it all got black, and—and—"

"there, now; don't try to think," advised the doctor. "you'll be all right in the morning."

"but i can't remember anything about that aviation man," protested mr. swift. "i never used to be that way—forgetting things. i don't like it!"

"oh, it's just because you're tired," declared the physician. "it will all come back to you in the morning. i'll stop in and see you then. now try to go to sleep." and he left the room.

tom followed him, mrs. baggert and mr. jackson remaining with the sick man.

"what is the matter with my father, dr. gladby?" asked tom earnestly, as the doctor prepared to take his departure. "is it anything serious?"

"well," began the medical man, "i would not be doing my duty, tom, if i did not tell you what it is. that is, it is comparatively serious, but it is curable, and i think we can bring him around. he has an affection of the heart, that, while it is common enough, is sometimes fatal.

"but i do not think it will be so in your father's case. he has a fine constitution, and this would never have happened had he not been run down from overwork. that is the principal trouble. what he needs is rest; and then, with the proper remedies, he will be as well as before."

"but that strange lapse of memory, doctor?"

"oh, that is nothing. it is due to the fact that he has been using his brain too much. the brain protests, and refuses to work until rested. your father has been working rather hard of late hasn't he?"

"yes; on a new wireless motor."

"i thought so. well, a good rest is what he needs, and then his mind and body will be in tune again. i'll be around in the morning."

tom was somewhat relieved by the doctor's words, but not very much so, and he spent an anxious night, getting up every two hours to administer the medicine. toward morning mr. swift fell into a heavy sleep, and did not awaken for some time.

"oh, you're much better!" declared dr. gladby when he saw his patient that day.

"yes, i feel better," admitted mr. swift.

"and can't you remember about mr. gunmore calling?" asked tom.

the aged inventor shook his head, with a puzzled air.

"i can't remember it at all," he said. "the minister is the last person i remember calling here."

tom looked worried, but the physician said it was a common feature of the disease from which mr. swift suffered, and would doubtless pass away.

"and you don't remember how we talked about me building a speedy aeroplane and trying for the ten-thousand-dollar prize?" asked tom.

"i can't remember a thing about it," said the inventor, with a puzzled shake of his head, "and i'm not going to try, at least not right away. but, tom, if you're going to build a new aeroplane, i want to help you. i'll give you the benefit of my advice. i think my new form of motor can be used in it."

"now! now! no inventions—at least not just yet!" objected the physician. "you must have a good rest first, mr. swift, and get strong. then you and tom can build as many airships as you like."

mr. swift felt so much better about three days later that he wanted to get right to work planning the airship that was to win the big prize, but the doctor would not hear of it. tom, however, began to make rough sketches of what he had in mind changing them from time to time. he also worked on a type of motor, very light, and modeled after one his father had recently patented.

then a new idea came to tom in regard to the shape of his aeroplane, and he worked several days drawing the plans for it. it was a new idea in construction, and he believed it would give him the great speed he desired.

"but i'd like dad to see it," he said. "as soon as he's well enough i'll go over it with him."

that time came a week later, and with a complete set of the plans, embodying his latest ideas, tom went into the library where his father was seated in an easy-chair. dr. gladby had said it would not now harm the aged inventor to do a little work. tom spread the drawings out in front of his father, and began to explain them in detail.

"i really think you have something great there, tom!" exclaimed mr. swift, at length. "it is a very small monoplane, to be sure, but i think with the new principle you have introduced it will work; but, if i were you, i'd shape those wing tips a little differently."

"no, they're better that way," said tom pleasantly, for he did not often disagree with his father. "i'll show you from a little model i have made. i'll get it right away."

anxious to demonstrate that he was right in his theory, tom hurried from the library to get the model of which he had spoken. he left the roll of plans lying on a small table near where his father was seated.

"there, you see, dad," said the young inventor as he re-entered the library a few minutes later, "when you warp the wing tips in making a spiral ascent it throws your tail wings out of plumb, and so—"

tom paused in some amazement, for mr. swift was lying back in his chair, with his eyes closed. the lad started in alarm, laid aside his model, and sprang to his father's side.

"he's had another of those heart attacks!" gasped tom. he was just going to call mrs. baggert, when mr. swift opened his eyes. he looked at tom, and the lad could see that they were bright, and did not show any signs of illness.

"well, i declare!" exclaimed the inventor. "i must have dozed off, tom, while you were gone. that's what i did. i fell asleep!"

"oh!" said tom, much relieved. "i was afraid you were ill again. now, in this model, as you will see by the plans, it is necessary—"

he paused, and looked over at the table where he had left the drawings. they were not there!

"the plans, father!" tom exclaimed. "the plans i left on the table! where are they?"

"i haven't touched them," was the answer. "they were on that table, where you put them, when i closed my eyes for a little nap. i forgot all about them. are you sure they're missing?"

"they're not here!" and tom gazed wildly about the room. "where can they have gone?"

"i wasn't out of my chair," said mr. swift, "i ought not to have gone to sleep, but—"

tom fairly jumped toward the long library window, the same one from which he had leaped to pursue andy foger. the casement was open, and tom noted that the screen was also unhooked. it had been closed when he went to get the model, he was sure of that.

"look, dad! see!" he exclaimed, as he picked up from the floor a small piece of paper.

"what is it, tom?"

"a sheet on which i did some figuring. it is no good, but it was in with the plans. it must have dropped out."

"do you mean that some one has been in here and taken the plans of your new aeroplane, tom?" gasped his father.

"that's just what i mean! they sneaked in here while you were dozing, took the plans, and jumped out of the window with them. on the way this paper fell out. it's the only clue we have. stay here, dad. i'm going to have a look." and tom jumped from the library window and ran down the path after the unknown thief.