dr. kurtz looked as grave as did dr. gladby when he had made an examination of the patient. mr. swift was still in a semi-conscious condition, hardly breathing as he rested on the bed where they had placed him after the fire.

"vell," said the german physician, after a long silence, "vot is your obinion, my dear gladby?"

"i think an operation is necessary."

"yes, dot is so; but you know vot kind of an operation alone vill safe him; eh, my dear gladby?"

dr. gladby nodded.

"it will be a rare and delicate one," he said. "there is but one surgeon i know of who can do it."

"you mean herr hendrix?" asked dr. kurtz.

"yes, dr. edward hendrix, of kirkville. if he can be induced to come i think there is a chance of saving mr. swift's life. i'll speak to tom about it."

the two physicians, who had been consulting together, summoned the youth from another room, where, with mrs. baggert and mr. jackson he had been anxiously awaiting the verdict.

"what is it?" the young inventor asked dr. gladby.

the medical man told him to what conclusion he and his colleague had arrived, adding:

"we advise that dr. hendrix be sent for at once. but i need hardly tell you, tom, that he is a noted specialist, and his services are in great demand. he is hard to get."

"i'll pay him any sum he asks!" burst out the youth. "i'll spend all my fortune—and i have made considerable money of late—i'll spend every cent to get my father well! money need not stand in the way, dr. gladby."

"i knew that, tom. still dr. hendrix is a very busy man, and it is hard to induce him to come a long distance. it is over a hundred miles to kirkville, and it is an out-of-the-way place. i never could understand why dr. hendrix settled there. but there he is, and if we want him he will have to come from there. the worst of it is that there are few trains, and only a single railroad line from there to shopton."

"then i'll telegraph," decided tom. "i'll offer him his own price, and ask him to rush here as soon as he can."

"you had better let dr. kurtz and me attend to that part of it," suggested the physician. "dr. hendrix would hardly come on the request of some one whom he did not know. i'll prepare a telegram, briefly explaining the case. it is the sort of an operation dr. hendrix is much interested in, and i think he will come on that account, if for no other reason. i'll write out the message, and you can have eradicate take it to the telegraph office."

"i'll take it myself!" exclaimed tom, as he got ready to go out into the night with the urgent request. "is there any immediate danger for my father?" he asked.

"no; not any immediate danger," replied dr. gladby. "but the operation is imperative if he is to live. it is his one and only chance."

tom thought only of his father as he hurried on through the night. even the prospect of the great race, so soon to take place, had no part in his mind.

"i'll not race until i'm sure dad is going to get better," he decided. with the message to the noted specialist tom also sent one to mr. damon, telling him the news, and asking him to come to shopton. tom felt that the presence of the odd gentleman would help him, and mr. damon, who first intended to stay on at the swift home until he and tom departed for eagle park, had gone back to his own residence to attend to some business tom knew he would come in the morning, and mr. damon did arrive on the first train.

"bless my soul!" he exclaimed with ready sympathy, as he extended his hand to tom. "what's all this?" the young inventor told him, beginning with the fire that had been the cause of the excitement which produced the change in mr. swift.

"but i have great hopes that the specialist will be able to cure him," said tom, for, with the coming of daylight, his courage had returned to him. "dr. gladby and dr. kurtz depend a great deal on dr. hendrix," he said.

"yes, he certainly is a wonderful man. i have heard a great deal about him. i have no doubt but what he will cure your father. but about the fire? how did it start?"

"i don't know, but now that i have a few hours to spare before the doctor can get here, i'm going to make an examination."

"bless my penwiper, but i'll help you."

tom went into the house, to inquire of mrs. baggert, for probably the tenth time that morning, how his father was doing. mr. swift was still in a semi-conscious condition, but he recognized tom, when the youth stood at his bedside.

"don't worry about me, son," said the brave old inventor, as he took tom's hand. "i'll be all right. go ahead and get ready for the race. i want you to win!"

tears came into tom's eyes. would his father be well enough to allow him to take part in the big event? he feared not.

by daylight it was seen that quite a hole had been burned in the aeroplane shed. tom and mr. damon, accompanied by mr. jackson, walked through the place.

"and you say the fire broke out right after you had seen the mysterious airship hovering over the house?" asked the eccentric man.

"well, not exactly after," answered tom, "but within an hour or so. why do you ask?"

but mr. damon did not answer. something on the floor of the shed, amid a pile of blackened and charred pieces of wood, attracted his attention. he stooped over and picked it up.

"is this yours?" he asked tom.

"no. what is it?"

the object looked like a small iron ball, with a tube about half an inch in diameter projecting slightly from it. tom took it.

"why, it looks like an infernal machine or a dynamite bomb," he said. "i wonder where it came from? guess i'd better drop it in a pail of water. maybe eradicate found it and brought it here. i never saw it before. mr. jackson, please hand me that pail of water. we'll soak this bomb."

"there is no need," said mr. damon, quietly. "it is harmless now. it has done its work. it was that which set fire to your shed, and which caused the stifling fumes."

"that?" cried tom.

"yes. this ball is hollow, and was filled with a chemical. it was dropped on the roof, and, after a certain time, the plug in the tube was eaten through, the chemicals ran out, set the roof ablaze, and, dripping down inside spread the choking odors that nearly prevented you from getting out your aeroplane."

"are you sure of this?" asked the young inventor.

"positive. i read about these bombs recently. a german invented them to be used in attacking a besieged city in case of war."

"but how did this one get on my shed roof?" asked tom.

"it was dropped there by the mysterious airship!" exclaimed the odd man. "that was why the aeroplane moved about over your place. those in it hoped that the fire would not break out until you were all asleep, and that the shed and the humming-bird would be destroyed before you came to the rescue. some of your enemies are still after you, tom."

"and it was andy foger, i'll wager!" he cried. "he was in that aircraft! oh, i'll have a long score to settle with him!"

"of course you can't be sure it was he," said mr. damon, "but i wouldn't be a bit surprised but what it was. andy is capable of such a thing. he wanted to prevent you from taking part in the race."

"well, he sha'n't!" cried tom, and then he thought of his invalid father. they made a further examination of the shed, and discovered another empty bomb. then tom recalled having seen something drop from the mysterious aeroplane as it passed over the shed.

"it was these bombs," he said. "we certainly had a narrow escape! oh, wait until i settle my score with andy foger!"

as there would be but little use for the aeroplane shed now, if tom sent his craft off to the meet, it was decided to repair it temporarily only, until he returned.

accordingly, a big tarpaulin was fastened over the hole in the roof. then tom put a new wing tip on in place of the one that had been scorched. he looked all over his sky racer, and decided that it was in fit condition for the coming meet.

"i'll begin to take it apart for shipment, as soon as i hear from the specialist that dad is well enough for me to go," he said.

it was a few hours after the discovery of the empty bomb that tom saw dr. gladby coming along. the physician was urging his horse to top speed. tom felt a vague fear in his heart.

"i've got a message from dr. hendrix, tom," he said, as he stopped his carriage, and approached the lad.

"when can he come?" asked the young inventor, eagerly.

"he can't get here, tom."

"can't get here! why not?"

"because the railroad bridge has collapsed, and there is no way to come. he can't make any other connections to get here in time—in time to do your father any good, tom. he has just sent me a telegram to that effect. dr. hendrix can't get here, and..." dr. gladby paused.

"do you mean that my father may die if the operation is not performed?" asked tom, in a low voice.

"yes," was the answer.

"but can't dr. hendrix drive here in an auto?" asked the lad. "surely there must be some way of getting over the river, even if the railroad bridge is down. can't he cross in a boat and drive here?"

"he wouldn't be in time, tom. don't you understand, dr. hendrix must be here within four hours, if he is to save your father's life. he never could do it by driving or by coming on some other road, or in an auto. he can't make the proper connections. there is no way."

"yes, there is!" cried tom, suddenly. "i know a way!"

"how?" asked dr. gladby, thrilled by tom's ringing tones. "how can you do it, tom?"

"i'll go for dr. hendrix in my humming-bird."

"going for him would do no good. he must be brought here."

"and so he shall be!" cried tom. "i'll bring him here in my sky racer—if he has the nerve to stand the journey, and i think he has! i'll bring dr. hendrix here!" and tom hurried away to prepare for the thrilling trip.