Next morning the world read at its breakfast table that the Mississippi River had frozen over just below St. Louis, and that the water was rising rapidly. The river had frozen solidly up to the surface. The level rose, and the water started to flow over the top of the ice cake, only to be turned into ice as it did so. Hour by hour the level rose, and hour by hour the solid ice barrier rose with the water level. Men had tried to blast a way through for the rushing waters, but without effect. As fast as the water tried to flow through the opening made by a charge of dynamite it froze again and plugged the hole through which it was attempting to escape.

Hastily improvised levees were thrown up, but the water outstripped the efforts of the builders. The lower part of St. Louis was flooded, and a great part of the population made homeless. Then low-lying lands beside the river were gradually submerged. In twenty-four hours there were calls for help all along the upper part of the Mississippi Valley. The rising water had flooded immense areas of cultivated land, and even larger areas were threatened. In another day a thousand square miles of crops were under water, and the loss in live stock was assuming formidable proportions. The new cold bomb in New York harbor had crept up to the Battery, as Teddy had foreseen. The Norfolk cold bomb had exploded, fortunately without loss of life. Gibraltar had witnessed three almost simultaneous blasts, and was again free of ice, but the whole world knew that it was at the mercy of Varrhus.

Davis, Evelyn, and Teddy were discussing the matter dolefully. Davis had been coming to the laboratory daily in the hopes of hearing that Teddy had devised some plan for the frustration of Varrhus' ambitious schemes. Teddy found himself liking Davis immensely, but with a peculiarly illogical annoyance that Evelyn seemed to like him quite as well. When he had phoned her of his safety after the fight with Varrhus he could hear a flood of thankfulness in her voice, but when he saw her the next day she was almost distant. He saw traces of real anxiety on her face, but she had not been really natural until they had worked nearly all day on the silver bracelet, trying to find what had been done to the surface to give it its peculiar property of allowing heat to pass in one direction, but not in the other. They were as far as ever from the solution. Davis was quite ignorant of abstract chemistry or physics and could not join in their discussions, but Teddy fancied that he was much more interested in Evelyn than was necessary. He was annoyed to find that he resented it. He had always looked on Evelyn as a comrade, and he could not understand this feeling that took possession of him. It did not occur to him to speculate upon the fact that he found ideas coming to him much more readily when working by Evelyn's side, or that he rarely attempted anything without asking her opinion. Teddy had never thought much of romance, and he did not suspect how much Evelyn's companionship meant to him.

Davis was reiterating for the fortieth time his disappointment at Varrhus' getting away.

"We almost had him," he said disgustedly. "Our explosive bullets were playing all over his infernal flying machine. We'd have landed one in that little glass cabin of his and smashed him nicely in another minute, when he skipped off like that. And I'll swear to it we were doing a hundred and eighty miles an hour."

"He ran away from us pretty easily," said Teddy dismally. "Isn't there a faster machine than yours we could get hold of?"

"Nothing but a single-seater, and not so much faster at that," said Davis. "A hundred and ninety-five is the best even the latest single-seater combat planes will do at a low altitude."

"Even for a short burst of speed?" asked Evelyn.

"Diving, you'll run up faster than that," Davis explained. "When we went straight down after Varrhus, we must have gone over two hundred, but for straightaway work we've nothing that will catch Varrhus."

"What's the official speed record?" asked Evelyn, toying with a test tube. She looked singularly pretty in the long white apron she wore in the laboratory.

"Two hundred and fifteen, I think," said Davis. "Some Spanish aviator made it. He'd doped his gas with picric acid, though."

"What does that do?" asked Teddy quickly.

"It's explosive, and about doubles the force of your explosions. It eats your engines right up, though. They used to use it in motor-boat races until a rule was made against it. You see, an engine is ruined after twenty minutes or so, and it made the racing unfair for people who couldn't buy a new engine for every race."

Teddy's face grew thoughtful.

"Picric acid," he said meditatively. "Suppose we used it in the gas of your plane. Would we have a chance of catching Varrhus?"

"I don't know," Davis said thoughtfully. "I hardly think so. It would make our speed better, but if it were anything of a chase our motors would be ruined before we'd gone far."

"The acid attacks the steel of the cylinders and makes the bore too large?" Teddy seemed to be thinking rapidly.

"Yes. You lose all your compression."

Teddy looked at Evelyn.

"Suppose the pistons and the interiors of your cylinders were plated with platinum? Platinum is one of the hardest metals, and should stand up under a great deal of wear."

"Would platinum resist the attack of the acid?" Davis grew excited.

"Surely."

Davis jumped to his feet.

"Then we've got him! New piston rings will let you plate the cylinders without reboring them unless you're going to plate them heavily. Can you do the plating?"

"Try," said Teddy.

"We make a hundred and eighty with straight gasoline," said Davis excitedly. "With doped gas——How long will it take to fix my motors?"

"Four or five hours. We'll borrow the acid vats of some electro-plating concern. Evelyn will mix the solution of platinum salts. I'll go arrange to borrow the vats while you get your motors disassembled and brought here on a motor truck."

Teddy hastily began to put on his coat.

"You're going to try to fight Varrhus again?" asked Evelyn anxiously.

"Are we?" asked Davis cheerfully. "Just ask me! We are."

"You hit him several times in the last fight," said Evelyn faintly, "and it didn't do any good."

"We'll use armor-piercing bullets this time," said Davis exuberantly. "Or we may be able to mount a one-pounder automatic. I think the plane will stand it. And at worst we can ram him."

Evelyn turned a trifle pale. "That means you'll both be killed."

Davis smiled. "Maybe not. We'll take a chance anyway, won't we, Gerrod?"

Teddy nodded shortly. "I'm going to get Varrhus or he's going to get me," he said succinctly.

They started for the front door. The commissioner of police was just getting out of his car.

"News, most likely," said Teddy, and they waited.

The commissioner of police looked worried when he shook hands with Teddy.

"My men have been trying to trace that package that contained the bracelet," he told him, "and have found that it was put in a country rural-delivery mail box after dark. The mail carrier took it when he made his morning route. There's absolutely no way of tracing it any farther. Any one might have passed by in an automobile and have put it in. The farmer in whose box it was is above suspicion. Now another set of letters has been sent in the same way from another rural-delivery box a hundred miles from the first. One is addressed to Miss Hawkins. I have it here. The postal authorities called me in when they saw the envelope."

He showed a huge yellow envelope addressed to Evelyn. In one corner was a large return card. "The Dictatorial Residence."

"It might be almost anything," said Davis. "Better not let Miss Hawkins open it. I'll do it, Gerrod."

Teddy shook his head.

"We'll tell her about it, and I'll open it in the laboratory."

Evelyn and Davis waited apprehensively until Teddy emerged from that room.

"No cold bombs, no electric shocks, and no poison gas," he said, smiling. "Just a billet doux to Evelyn. It fits in beautifully with our plans, Davis."

Evelyn took the sheet he extended to her, and read:

The Dictatorial Residence, August 29th.

His Excellency Wladislaw Varrhus, dictator of the earth, has been much annoyed by the efforts of one Theodore Gerrod to obstruct his plans and desires. He has been informed through the press of the fact that Miss Evelyn Hawkins has collaborated with and encouraged Theodore Gerrod in his rash attempts. His excellency the dictator is pleased to require that Miss Evelyn Hawkins repair to a spot some five miles due east from Norman's Reef, off the coast of Maine. Miss Hawkins may bring with her a maid and such baggage as she may require. She is to be held as security for the cessation of Theodore Gerrod's efforts to impede the secure establishment of the dictatorship. The Mississippi River has been closed to traffic, and will remain closed until this order has been obeyed by Miss Hawkins. The time set for Miss Hawkins' appearance at that spot is daybreak of Tuesday, September the third. Given at the dictatorial residence.

Wladislaw Varrhus.

Evelyn looked at the three men with a white face. The commissioner of police looked grave. Davis was smiling, and Teddy was smiling, too, but with a blaze of anger in his eyes.

"Gerrod," said Davis whimsically, "I am much depressed that Varrhus didn't include me with you as making efforts to obstruct his plans and desires."

"The government will have to be notified," said the commissioner of police solemnly.

"Do—do you think I had better go?" asked Evelyn hesitatingly.

"No!" exploded Teddy and Davis together. Teddy went on: "Why, Evelyn, the man is insane! And besides we've just thought of something that's sure to get him. We'll lay in wait for him, and then he'll walk into our parlor nicely. When he does———"

"Finis," said Davis cheerfully, "if I may borrow a phrase from the French."

"And if it's a long chase," said Teddy even more cheerfully, "the dear person set the time for dawn, and we'll have light to fight by. Let's go and set to work on that plane of yours."

They left together in high spirits. Evelyn stood quite still after they had gone, absently crushing the letter from Varrhus in her hand. Presently, with a sob, she went to her room and allowed herself to cry. They would not let her face danger, but Teddy was going out to fight, perhaps to die—and for her.

Over at the hangar, mechanics swarmed upon the fighting plane, dismounting the motors and disassembling them. The cylinders and pistons were being carefully packed. A big motor truck had already backed up at the wide door of the aËroplane shed, and as fast as the parts were packed they were loaded on it. Davis was here, there, and everywhere. He had asked permission for the experiment, and it has been granted. The government was prepared to risk almost anything rather than allow Varrhus to succeed in his huge blackmailing of the entire human race. There was no hesitation in allowing anything that might afford a fighting chance of downing the black flyer. The Mississippi floods were growing in size and destructiveness. The New York cold bomb, dropped the night Teddy and Davis had fought the black machine over the harbor, was expected to explode at any moment. Every window still intact in the city had been pasted with strips of paper to keep the fragments from becoming a menace to those on the streets when the bomb should burst them.

Davis had conferred with the commandant of the forts, and volunteers had been asked for among the garrison. A boat was being heavily armed with concealed guns. It would go to the point where Varrhus would expect Evelyn to be taken. He would see the small boat, drop down to take Evelyn on board his evil craft, and the masked batteries of anti-aircraft guns would open on him in a blast of fire. Teddy's discovery that flares fired into the cloud of liquified gas would cause it to burn harmlessly in mid-air had been adapted to protect the crew. As the guns opened on the hovering black flyer a stream of fire balls would be made to float overhead to set flaming the stream of liquid hydrogen Varrhus might be expected to shoot downward. At that, though, the mission of the boat crew was hazardous in the extreme.

The telephone rang in the hangar. Teddy was on the wire. He had commandeered the big wooden acid vats of an electro-plating plant, and the platinum-plating solution was being mixed even then. If Davis brought the motors over in parts, the plating might begin immediately.

The big truck rumbled off, Davis smiling confidently on the seat beside the chauffeur. Half a dozen mechanics perched on various parts of the load. When the truck stopped before the electro-plating plant they leaped off and rushed the glistening cylinders inside. In twenty minutes they were in the plating solution and an almost infinitely thin film of platinum was slowly forming within them.

The workmen of the electro-plating plant labored far into the night on their task. Teddy had insisted that a film of platinum ten times the thickness of the usual precious-metal plating be used, and the process was slow. When the cylinders had been prepared, the pistons remained, and the exhaust ports and valves. These, too, were coated with the hard, acid-resisting metal, and Davis' mechanics began their task of fitting piston rings to the altered motor parts. The rings themselves had then to be plated, and all the plating burnished and polished. Teddy and Davis snatched a few hours' sleep while the motor in its disassembled state was being carried back to the hangar and re-installed in the aËroplane. They woke, and during all the following day Davis sat in the pilot's seat, listening with a practiced ear and aiding in the final tuning up of the changed motors, adjusting the carburetors to their new fuel. Thirty per cent of picric acid added to the finest, highest grade gasoline was to be used. No one had dared use such a percentage before, even for motors that were expected to be ruined.

Teddy, in the meantime, was familiarizing himself with the small one-pounder automatic gun—similar to the German antitank weapons—that was to be installed in the bow of the aËroplane. By nightfall all was finished. Teddy ran over to New York and saw Evelyn for the last time before making his attempt, and the next morning he and Davis flew to Noman's Reef, where a camouflaged hangar had been erected on telegraphed instructions from New York. Tuesday dawn found them alert and anxiously scanning the sky for a sign of the black flyer.