Moreover, he'd become a kind of father figure for her, an advisor in matters both professional and personal, the man she went to when she was in trouble.

He was in his fifties, a widower with three kids who were all off on their own. He was mildly overweight, with that washed-out look that people have who've recently lost fifty or so pounds. Chandler had suffered a severe heart attack the previous Christmas and had been put on a stringent diet.

Evelyn, anxious to help this closest of friends, had gone farther: She'd inquired whether the light lunar gravity wouldn't help Chandler by easing the strain on his damaged heart. There'd been talk all along of providing a sanctum sanctorum on the Moon for heart patients, and this seemed a good way to get the ball rolling. The disadvantage was that his physician didn't think he'd ever be able to return groundside again.

Chandler was more than willing. So Evelyn had gotten the director she wanted, and simultaneously performed an act of kindness for a man to whom she was indebted. Did he feel better? "Twenty years younger," he said. "I'd gotten to a point that it was like having a lump of lead in my chest." He beamed at her. "The weight's gone."

They were debating the merits of the applicants on the short list for his assistant's job when the phone rang. "It's Orly Carpenter, Mr. Chandler," the secretary's voice said. "He wants to speak with Dr. Hampton."

Carpenter was the NASA operations director at Houston. Chandler passed the phone.

"Good morning, Orly," said Evelyn. "How's everything?"

"Not good." Carpenter was an ex-astronaut whose voice tended to flatten when he was reporting trouble. "We've got a situation," he said.

She was seated on the edge of the desk, watching the Boston street scene that played across one wall of the director's office. People with umbrellas were moving through a sudden rain storm. "What is it?" she asked casually. Orly was okay, but she knew from long experience that government types in general tend to overreact to problems.

"You know about the comet," he said.

"Of course."

"We think it's going to hit. It's big, and it's coming fast. My God, Evelyn, we've only got three and a half days."

"Relax, Orly," she said, smothering her own sudden alarm. "I'm putting you on the speaker. Jack Chandler's here."

Chandler shared her view of government alarm. He said hello.

"The thing's going to hit what?" asked Evelyn. "The Earth? One of the stations? What?"

"The Moon." He caught his breath. "The Moon. It's going to give you one hell of a whack."

"You're not serious."

"Do I sound as if I'm not serious?"

"When?"

"Saturday night. Late in the evening, looks like."

"How sure are you?"

"About ninety-eight percent."

Evelyn tried to collect her thoughts. "You're talking as if it's something we need to worry about. Is it going to hit near Moonbase?"

"Looks like Mare Muscoviense."

"The observatory," whispered Jack. "Is it going to take out the observatory?"

"At the very least. This thing's going to trigger major quakes. Maybe worse."

"What could be worse?" asked Evelyn.

"There's a distinct possibility it could shatter the Moon."

Shatter the Moon. The phrase hung in the still air. Evelyn stared at sheets of rain battering the Prudential Building, trying to understand what he was really saying. "How do you mean," asked Evelyn, "shatter?"

"How else do you want me to say it? Think of a bag of loose rock."

Evelyn picked up a pad and began to scribble. They had three moonbuses, which among them could carry forty people out to L1. Round-trip took a little over five hours. Between now and ten thirty Saturday night they could make seventeen round-trips.

"Jack," she said, "how many people do we have at Moonbase now?"

He was already working on it. "Seven hundred thirty-four," he read off his screen. "Plus twelve on their way from L1."

Evelyn stared at him.

"I don't think we can get them all off," he said.

Ronald Reagan Washington National Airport, Washington, D.C. 8:47 A.M.

The SSTO Arlington was about a half hour from launch. George Culver tried to concentrate on his checkoff sheet. He'd finally scored with Annie last night and his mind was filled with images of her. In back, he could hear the passengers beginning to come on board. He shook himself and tried again to read his instruments.

The Single Stage To Orbit space plane had capacity for two hundred thirty-five passengers, and usually carried a crew of twelve. It was slightly more compact than ordinary jumbo airliners, and baggage restrictions were far tighter. But contrasted with the old shuttles, it constituted a remarkably cheap and efficient means of getting into orbit.

George had started his career as a carrier pilot. He'd flown the A-77 Blackjack jet, had become a squadron commander, gotten married, and made the jump to civilian aviation. In all, he'd married three times-all medical types, one physician, one nurse, one hospital systems analyst. He'd gotten bored with each, and had pulled the plug on all three. His wives didn't seem to be all that upset when it happened, and the marriages had ended more or less amicably. None had lasted two years.

He was just finishing with the preliminary readouts when Mary Casey, his copilot, strolled onto the flight deck and sat down.

"How we doing, Mary?" he asked.

"Guidance wasn't lining up," she said. "I put in another box."

He nodded, reached for his clipboard, and gazed at the manifest. "How's Billy?"

Billy was her son. He was a teenager now, just learning to drive, just beginning to assert his independence. His grades were down, and George knew that Mary was unhappy with his choice of friends. "He's been better," she said.

The plane was only three-quarters full, not unusual for a Wednesday morning. There were some vacationers among the passengers, but not many. Fares to the space station were still high, and despite its obvious attractions, Skyport remained out of range for persons of moderate means. But the Lunar Transport Authority, a semiautonomous corporation, was promising that costs would come down dramatically with the planned arrival next year of the second-generation SSTO.

Mary pulled on her headset and adjusted the mike, still talking about Billy.

The captain listened politely. "All part of growing up," he said. "I bet you weren't easy to handle."

The SSTO flew three times weekly from Reagan to the space station. George's crew also made occasional direct runs from Reagan to Moscow, Rome, and London. But this was the flight they enjoyed, riding the thrusters all the way into orbit.

Mary tapped the mike. "Tower," she said, "this is Flight One-seventeen. Comm check."

"Flight One-seventeen," returned a female voice in their earphones. "Check is five by."

"Where's Curt?" asked George.

"Right here, Captain." The flight engineer poked his head in. "Just getting my coffee."

The flight to Skyport would take one hour, forty-three minutes. They'd unload, refuel, pick up returning passengers and cargo, and be back in time for a late lunch.

Mary finished her procedure. George handed her the passenger list and pointed at a couple of names. Big-time singers. She also recognized a well-known TV critic and an Arab oil dealer. There were some kids back there, too. Headed for the vacation of their lives. And a couple of families were going all the way to Moonbase.

"Flight One-seventeen, Tower." Same female voice.

"Go ahead, Tower."

"Your flight is cancelled. Unload your passengers and stand by."

Mary frowned at the captain, who had not yet put on his earphones. She switched on the speaker. "Say again, Tower."