During the four-day period bracketing the ideal instant of departure ships leaving Leyport paid a fancy premium for the privilege over and above the standard service fee. Only a large ship could afford such a fee; the saving in cost of single-H reactive mass had to be greater than the fee. The Rolling Stone had departed just before the premium charge went into effect; consequently she had trailing her like beads on a string a round dozen of ships, all headed down to Earth, to tack around her toward Mars.

If the Rolling Stone vectored back and shaped course for Luna rather than Mars, there was a possibility of traffic trouble.

Collisions between spaceships are almost unheard of; space is very large and ships are very tiny. But they are possible, particularly when many ships are doing much the same thing at the same time ia the same region of space. Spacemen won't forget the Rising Star and the patrol vessel Trygve Lie - four hundred and seven dead, no survivors.

Ships for Mars would be departing Luna for the next three days and more; the Rolling Stone, in rounding Earth and head­ing back to Luna (toward where Luna would be on her arrival) would cut diagonally across their paths. Besides these hazards, there were Earth's three radio-satellites and her satellite space station; each ship's flight plan, as approved by Luna Pilot Station, took into consideration these four orbits, but the possible emergency maneuver of the Rolling Stone had had no such safety check. Roger Stone mentally chewed his nails at the possibility that Traffic Control might refuse permission for the Rolling Stone to change its approved flight plan - which they would do if there was the slightest possibility of collision, sick child or no.

And Captain Stone would ignore their refusal, risk collision and take his child home - there to lose his pilot's license certainly and to face a stiff sentence from the Admiralty court possibly.

Besides the space station and the radio satellites there were the robot atom-bomb peace rockets of the Patrol, circling the Earth from pole to pole, but it was most unlikely that the Rolling Stone's path would intersect one of their orbits; they moved just outside the atmosphere, lower than a spaceship was allowed to go other than in landing, whereas in order to tack the Rolling Stone would necessarily go inside the orbits of the radio satellites and that of the space station wait a minute - Roger Stone thought over that last idea. Would it be possible to match in with the space station instead of going back to Luna?

If he could, he could get Lowell back to weight a couple of days sooner - in the spinning part of the space station!

The ballistic computer was not in use; Castor and Hazel were still in the tedious process of setting up their problems. Captain Stone moved to it and started making a rough set-up directly on the computer itself, ignoring the niceties of ballistics, simply asking the machine, "Can this, or can this not, be done?"

Half an hour later he gave up, let his shoulders sag. Oh, yes, he could match in with the space station's orbit - but at best only at a point almost a hundred degrees away from the station. Even the most lavish expenditure of reaction mass would not permit him to reach the station itself.

He cleared the computer almost violently. Hazel glanced toward him. "What's eating you, son?"

"I thought we might make port at the station. We can't."

"I could have told you that"

He did not answer but went aft. Lowell, he found, was as sick as ever.

Earth was shouldering into the starboard port, great and round and lovely; they were approaching her rapidly, less than ten hours from the critical point at which they must maneuver, one way or the other. Hazel's emergency flight plan, checked and rechecked by the Captain, had been radioed to Traffic Con­trol. They were all resigned to a return to Luna; nevertheless Pollux was, with the help of Quito Pilot, Ecuador, checking their deviations from the original flight plan and setting up the problem of preparing a final ballistic for Mars.

Dr. Stone came into the control room, poised near the hatch, caught her husband's eye and beckoned him to come with her.

He floated after her into their stateroom. "What is it?" he asked. "Is Lowell worse?"

"No, he's better."

"Eh?"

"Dear, I don't think he was spacesick at all."

"What's that?"

"Oh, a little bit, perhaps. But I think his symptoms were largely allergy; I think he is sensitive to the sedative."

"Huh? I never heard of anyone being sensitive to that stuff before."

"Neither have I, but there can always be a first time I withdrew the drug several hours ago since it did not seem to help him. His symptoms eased off gradually and his pulse is better now."

"Is he okay? Is it. safe to go on to Mars?"

"Too early to say. I'd like to keep him under observation another day or two."

"But - Edith, you know that's impossible. I've got to maneu­ver." He was wretched from strain and lack of sleep; neither had slept since blast-off more than twenty-four hours earlier.

"Yes, I know. Give me thirty minutes warning before you must have an answer. I'll decide then."

"Okay. I'm sorry I snapped at you."

"Dear Roger!"

Before they were ready to 'round the corner' on their swing past Earth the child was much better. His mother kept him under a light hypnotic for several hours; when he woke from it he demanded food. She tried letting him have a few mouth­fuls of custard; he choked on the first bite but that was simply mechanical trouble with no gravity - on the second bite he learned how to swallow and kept it down.

He kept several more down and was still insisting that he was starved when she made him stop. Then he demanded to be untied from the couch. His mother gave in on this but sent for Meade to keep him under control and in the bunk-room. She pulled herself forward and found her husband. Hazel and Castor were at the computer; Castor was reading off to her a problem program while she punched the keys; Pollux was taking a doppler reading on Earth. Edith drew Roger Stone away from them and whispered, "Dear, I guess we can relax. He has eaten - and he didn't get sick."

"Are you sure? I wouldn't want to take even a slight chance."

She shrugged. "How can I be sure? I'm a doctor, not a fortune-teller."

"What's your decision?"

She frowned, "I would say to go on to Mars."

"It's just as well." He sighed. "Traffic turned down my alternate flight plan. I was just coming back to tell you."

"Then we have no choice."

"You know better than that. I'd rather tell it to the judge than read the burial service. But I have one more card up my sleeve."

She looked her query; he went on. "The War God is less than ten thousand miles behind us. If necessary, by using our mass margin, in less than a week I could match with her and you and the baby could transfer. She's a "tumbling. pigeon" since they refitted her - anything from Luna-surface to a full gravity."

"I hadn't thought of that. Well, I don't think it will be neces­sary but it's a comfort to know that there is help close by." She frowned. "I would not like to leave you and the children to shift for yourselves - and besides, it's risky to use your margin; you may need it badly when we approach Mars."

"Not if we handle the ship properly. Don't you worry; Hazel and I will get it there if we have to get out and push."

Pollux had stopped what he was doing and had been trying to overhear his parents' conversation. He was unsuccessful; they had had too many years' practice in keeping the kids from hearing. But he could see their intent expressions and the occa­sional frowns; he signaled his twin.