"Christ, Chucky, lower your voice," said the second scientist, moodily stirring his cup.

"I've worked with the sentinels," the first scientist said. "I know what they're capable of. This might be our only chance to-"

"And I just finished wrapping up what's left of Marble One," the man named Chucky shot back. "Trashed beyond recognition. Three of my friends, dead. I tell you, we're not ready for this. We're overextended down here."

"What happened to Marble One is a terrible thing," said the first scientist. "And it's okay to grieve. But don't let grief blind you to the larger issue: why we're down here. No advance was ever made without risk. These visitors clearly want to help us. They have so much to teach-"

"How the hell do you know they want to teach us anything?" Chucky demanded.

"If you'd seen how beautiful the markers are, how utterly-"

"So what? A black panther's beautiful, too…right up to the minute it rips your guts out."

The scientist sniffed. "That's an inappropriate comparison."

"The hell it is. You assume they're friendly. You think you know everything. Let me tell you something: nature is never friendly. Our own planet is full of life-forms, all busy trying to kill each other!" The machinist's voice was beginning to rise again.

"Don't blame others for the failings of our planet," said the first scientist.

"Maybe they seeded planets all over the universe with these things." Chucky's face was pale, and his hands shook slightly. "We uncover 'em, they beam a signal back to their masters-who then come and destroy us. Very efficient system for wiping out potential competition."

The second scientist shook his head. "That's a little paranoid, don't you think?"

"Paranoid? Then you explain what's happening here. All the accidents, the problems nobody wants to talk about!"

"Cool it," the petty officer growled.

Chucky stood up, knocking his chair over. "Then why are people dying? Why are people getting sick? Why am I getting sick? Because there's something wrong, something wrong with my head…"

Crane was about to step forward and intervene when, suddenly, the machinist fell silent. He righted his chair and sat down, the petty officer's restraining hand on his shoulder.

Commander Korolis had just entered the cafeteria, accompanied by two officers in black fatigues and combat boots.

For a moment, all was still. The only noise was the machinist's labored breathing.

The commander turned his pale, out-of-synch eyes toward Crane, and his expression hardened into disapproval. Then he turned his gaze to the group at the table, moving slowly from one person to the next, as if committing each face to memory. And then-very slowly and deliberately-he turned and walked out again without saying a word.

32

Three hours later, the summons from Asher came. Michele Bishop had left the deck 4 infirmary to oversee the electroencephalograms Crane requested, and he'd just finished logging the morning's events and was preparing to track down "Chucky," the machinist, for a mandatory physical and psychological evaluation when the telephone rang.

He walked across the small room, plucked the phone from its cradle. "Dr. Crane speaking."

"Peter? This is Howard Asher. I need your assistance, please."

"Of course. Are you in your office? I'll be right there-"

"No. I'm in Hyperbaric Therapy. Deck seven. You know the location?"

"Certainly. But-"

"Please come at once." The phone went dead.

Crane stared at the receiver in mystification. Why Asher would be there, of all spots, made no sense.

It was the work of ten minutes to pass through the Barrier and ascend to deck 7. The scientific level was full of activity, as usual, but the small suite of rooms on the dead-end corridor composing Hyperbaric Therapy was empty, almost ghostly. This, too, was expected: since the atmosphere on the Facility was not, in fact, pressurized in any way, there were no pressure-related ailments to be treated. Crane had found this out the hard way, with his original theory of caisson disease.

The therapy suite consisted of a tiny control room; a waiting area outside the hyperbaric chamber; and the chamber itself, a metal cylinder about six feet in diameter and ten feet long, with an observation porthole in the entrance hatch and another on one side. Within, two cushioned benches ran along each of the walls, set across from each other. Along the ceiling ran two identical control strips, housing the lighting as well as the emergency water deluge system.

Asher was standing in the waiting area, along with John Marris, the NOD cryptanlyst. Marris had a large satchel slung over one shoulder. Asher looked tired, almost haggard, and his left hand-which he held protectively against his side-was bandaged with gauze. He nodded distractedly at Crane as he entered.

"You're not looking especially good," Crane said. "Getting enough sleep?"

Asher's response was a wintry smile.

Crane nodded at the bandaged hand. "What happened?"

"Look for yourself. Gently, please." Asher turned to Marris. "We'll run those common-language routines once again, doubling the ply depth. Perhaps we'll get a different result."

Carefully, Crane unhooked the metal butterfly clip and unwrapped the bandage. Beneath the gauze, an evil-looking ulceration had formed on the back of Asher's hand.

Crane examined it closely. The surrounding skin was pale, almost alabaster. Yet-alarmingly-Asher's fingertips were bluish black around the nails.

"When did you notice this?" he asked, looking up sharply at the chief scientist.

"Last night."

"Well, it's no joke." Crane carefully rewrapped the bandage. "It's a result of the vascular insufficiency you're suffering from. Not only is the hand ulcerated now, but there are signs of incipient necrosis as well. You have to report to the Medical Suite. We need to run Doppler imaging on that hand, do a bypass procedure on the blockage-"

"No!" Asher said fiercely. He took a deep breath, got himself under control. "No. There's no time for surgery."

Crane looked at him appraisingly. "Why is that?"

"We need to decipher that code. Three men just died; it's vital we understand what the message is. Do you hear, Peter? Until we've done that, I can't afford the downtime."

Crane frowned. "But your hand-"

"I'm still taking Coumadin. When I got my hand bandaged in Medical this morning, the on-duty intern gave me a course of antibiotic therapy. And there's this." Asher waved in the direction of the Chamber.

Crane had wondered if this might be what Asher had in mind. Hyperbaric therapy was, in fact, often used as an adjunctive treatment for clinical conditions like arterial insufficiency or for necrotizing soft tissue infections. Pure oxygen, under pressure, penetrated tissue more effectively, rallied white blood cells to the body's defense. Yet it was no substitute for more aggressive, and more direct, treatment.

"Listen, Peter," Asher said, his voice growing low and persuasive. "We're close. It's thanks to you the sentinels are now transmitting on countless frequencies. That was a huge leap for us. And with different messages on each of the frequencies, we have that many more samples to work with. See, the trouble was we've been barking up the wrong tree for the last couple of days."

"How so?"

"We thought we'd cracked it. We thought the sentinels had been transmitting…well, a mathematical expression."

"A mathematical expression?" Crane repeated. He found it hard to keep the disbelief out of his voice.

For a moment, Asher's look became almost sheepish. "A very simple mathematical expression."

"What was it?"