«Provided,» suggested Thuvan Dihn, «you do not chance to collide with some other night wanderer in the meanwhile.»

Carthoris smiled. «No danger of that,» he replied. «See here,» and he indicated a device at the right of the destination compass. «This is my 'obstruction evader,' as I call it. This visible device is the switch which throws the mechanism on or off. The instrument itself is below deck, geared both to the steering apparatus and the control levers.

«It is quite simple, being nothing more than a radium generator diffusing radio-activity in all directions to a distance of a hundred yards or so from the flier. Should this enveloping force be interrupted in any direction a delicate instrument immediately apprehends the irregularity, at the same time imparting an impulse to a magnetic device which in turn actuates the steering mechanism, diverting the bow of the flier away from the obstacle until the craft's radio-activity sphere is no longer in contact with the obstruction, then she falls once more into her normal course. Should the disturbance approach from the rear, as in case of a faster-moving craft overhauling me, the mechanism actuates the speed control as well as the steering gear, and the flier shoots ahead and either up or down, as the oncoming vessel is upon a lower or higher plane than herself.

«In aggravated cases, that is when the obstructions are many, or of such a nature as to deflect the bow more than forty-five degrees in any direction, or when the craft has reached its destination and dropped to within a hundred yards of the ground, the mechanism brings her to a full stop, at the same time sounding a loud alarm which will instantly awaken the pilot. You see I have anticipated almost every contingency.»

Thuvan Dihn smiled his appreciation of the marvellous device. The forward servant pushed almost to the flier's side. His eyes were narrowed to slits.

«All but one,» he said.

The nobles looked at him in astonishment, and one of them grasped the fellow none too gently by the shoulder to push him back to his proper place. Carthoris raised his hand.

«Wait,» he urged. «Let us hear what the man has to say-no creation of mortal mind is perfect. Perchance he has detected a weakness that it will be well to know at once. Come, my good fellow, and what may be the one contingency I have overlooked?»

As he spoke Carthoris observed the servant closely for the first time. He saw a man of giant stature and handsome, as are all those of the race of Martian red men; but the fellow's lips were thin and cruel, and across one cheek was the faint, white line of a sword-cut from the right temple to the corner of the mouth.

«Come,» urged the Prince of Helium. «Speak!»

The man hesitated. It was evident that he regretted the temerity that had made him the centre of interested observation. But at last, seeing no alternative, he spoke.

«It might be tampered with,» he said, «by an enemy.»

Carthoris drew a small key from his leathern pocket-pouch.

«Look at this,» he said, handing it to the man. «If you know aught of locks, you will know that the mechanism which this unlooses is beyond the cunning of a picker of locks. It guards the vitals of the instrument from crafty tampering. Without it an enemy must half wreck the device to reach its heart, leaving his handiwork apparent to the most casual observer.»

The servant took the key, glanced at it shrewdly, and then as he made to return it to Carthoris dropped it upon the marble flagging. Turning to look for it he planted the sole of his sandal full upon the glittering object. For an instant he bore all his weight upon the foot that covered the key, then he stepped back and with an exclamation as of pleasure that he had found it, stooped, recovered it, and returned it to the Heliumite. Then he dropped back to his station behind the nobles and was forgotten.

A moment later Carthoris had made his adieux to Thuvan Dihn and his nobles, and with lights twinkling had risen into the star-shot void of the Martian night.

As the ruler of Ptarth, followed by his courtiers, descended from the landing-stage above the palace, the servants dropped into their places in the rear of their royal or noble masters, and behind the others one lingered to the last. Then quickly stooping he snatched the sandal from his right foot, slipping it into his pocket-pouch.

When the party had come to the lower levels, and the jeddak had dispersed them by a sign, none noticed that the forward fellow who had drawn so much attention to himself before the Prince of Helium departed, was no longer among the other servants.

To whose retinue he had been attached none had thought to inquire, for the followers of a Martian noble are many, coming and going at the whim of their master, so that a new face is scarcely ever questioned, as the fact that a man has passed within the palace walls is considered proof positive that his loyalty to the jeddak is beyond question, so rigid is the examination of each who seeks service with the nobles of the court.

A good rule that, and only relaxed by courtesy in favour of the retinue of visiting royalty from a friendly foreign power.

It was late in the morning of the next day that a giant serving man in the harness of the house of a great Ptarth noble passed out into the city from the palace gates. Along one broad avenue and then another he strode briskly until he had passed beyond the district of the nobles and had come to the place of shops. Here he sought a pretentious building that rose spire-like toward the heavens, its outer walls elaborately wrought with delicate carvings and intricate mosaics.

It was the Palace of Peace in which were housed the representatives of the foreign powers, or rather in which were located their embassies; for the ministers themselves dwelt in gorgeous palaces within the district occupied by the nobles.

Here the man sought the embassy of Dusar. A clerk arose questioningly as he entered, and at his request to have a word with the minister asked his credentials. The visitor slipped a plain metal armlet from above his elbow, and pointing to an inscription upon its inner surface, whispered a word or two to the clerk.

The latter's eyes went wide, and his attitude turned at once to one of deference. He bowed the stranger to a seat, and hastened to an inner room with the armlet in his hand. A moment later he reappeared and conducted the caller into the presence of the minister.

For a long time the two were closeted together, and when at last the giant serving man emerged from the inner office his expression was cast in a smile of sinister satisfaction. From the Palace of Peace he hurried directly to the palace of the Dusarian minister.

That night two swift fliers left the same palace top. One sped its rapid course toward Helium; the other-

Thuvia of Ptarth strolled in the gardens of her father's palace, as was her nightly custom before retiring. Her silks and furs were drawn about her, for the air of Mars is chill after the sun has taken his quick plunge beneath the planet's western verge.

The girl's thoughts wandered from her impending nuptials, that would make her empress of Kaol, to the person of the trim young Heliumite who had laid his heart at her feet the preceding day.

Whether it was pity or regret that saddened her expression as she gazed toward the southern heavens where she had watched the lights of his flier disappear the previous night, it would be difficult to say.

So, too, is it impossible to conjecture just what her emotions may have been as she discerned the lights of a flier speeding rapidly out of the distance from that very direction, as though impelled toward her garden by the very intensity of the princess' thoughts.

She saw it circle lower above the palace until she was positive that it but hovered in preparation for a landing.