Captain Philip Mackenzie, of the Space Transport Jimmy Carter, had been mostly dead for seventy-eight days -- that's what his heads-up display said. But seventy-eight days? His first scheduled wakeup was for the slingshot around Jupiter and that was two years out. So why was he awake now?

He unhooked himself from his stasis tube, wincing at the quick pain as he pulled out tubes and unhooked wires from sensitive parts of his anatomy. He unbuckled his harness and gently nudged himself off the tube bed.

"Mother," he croaked, "what happened? Why did you wake me so soon?"

"THERE HAS BEEN A FATALITY IN POD ONE," the computer replied.

"A colonist is dead? Are you sure?"

"CONFIRMED."

"How? What cause?"

"UNKNOWN AT THIS TIME."

"Mother, activate life support and emergency lighting in Pod One and the main corridor," he ordered.

He floated across the room and pulled his uniform from his locker. When he finished dressing, he made his way down the dimly lit central corridor to the rear of the ship.

Every available inch of hull in Pod One was covered with stasis tubes: Tube after tube, end to end, side by side. There were two hundred and fifty of them in this pod and there were four pods on the ship.

Mackenzie looked at the faces of his sleeping cargo as he floated past their tubes; men, women and children -- all in diapers. He didn't look too closely at the women, not out of prudishness -- the sight of a woman's breasts didn't bother him in the least -- but each female form, each woman's face, reminded him of Victoria and that hurt.

He was half-way down the pod before he found it: a small red light, blinking in the half-light from its perch atop a tube. The man inside was in his late forties, maybe early fifties, with dark, almost black skin, deep set eyes and a high forehead topped off with a shock of gray, almost white hair.

He ordered a cursory medical summary from the tube: The reported time of death was fifteen mission days, sixty-seven minutes. This was day seventy-eight. Mackenzie should have notified immediately, so why had Mother just now revived him?

"Mother," he said as touched his comm badge, "access the passenger manifest and give me a holo summary for Pod One, tube one twenty-three. I'm on my way."

When he arrived in Operations he was greeted by an exact likeness of the dead man floating in the mist of the holo-tank.

"Hello," it said. "I'm Dr. Samuel R. Goodwin. I'm fifty-three years old. Born in Arvada, Colorado, USA, September 10, 2047. I'm Executive Director of Sagan Four...."

"Stop!" Mac commanded. The image froze.

Sagan Four was a ten kilometer long cylinder spinning just this side of the Oort Cloud; a generation ship, built to traverse light-years of empty space -- the first of its kind, mankind's best hope for survival. Mac's sleepers were Sagan's crew and Sam Goodwin was Executive Director. And now he was dead.

Mackenzie flew to the crew's tube room.

Sleepers wake from stasis in different ways; some wake up a piece at a time, others wake up with the shakes, vomiting and shivering violently. Then there are those who wake up calm and collected, as if just roused from a good night's sleep. Lieutenant Carlton Reeves, newly assigned Second Officer to the Jimmy Carter, woke with a start and a gasp, filling his diaper before he could regain control of his bowels.

"What?" he whispered.

"Quiet, kid," Mac ordered. "Don't talk." He gave Reeves a squeeze-bulb of electrolytes. "Suck on this while I unhook you."

Reeves drank as Mac removed the tangle of wires and tubes from the boy's body. Reeves was young, early twenties maybe. This was probably the boy's first deep space mission, judging by the mess he made in his diaper.

"Do you know where you are?" Mac asked.

Reeves nodded stiffly.

"Good. I'm going to undo your harness now," Mackenzie said as he removed the last of the wires. "Clean yourself up. I need you in Pod One in fifteen minutes. Do you understand?"

The young lieutenant nodded again and looked down at his soiled diaper. "Sorry," he croaked.

"Fifteen minutes," Mac repeated as he sailed out into the corridor.

Reeves floated in to Pod One almost twenty minutes later.

"Sir?" Reeves said sheepishly. "May I ask why you woke me?"

Mac didn't look up from his work. "I need you to run diagnostics on this tube's processor and on Mother," he said. "I want to know why this man died and I want to know why Mother didn't inform me."

"He's dead?" The boy asked as he moved closer to the tube, looking in at the late Doctor Goodwin.

Mac nodded. "I want a full level-three software diagnostic. I also want a full communications check between Mother and this tube."

"But a level-three will take hours!" Reeves protested.

"Do you have something better to do, Lieutenant?" Mac snapped.

"No, Sir," the lieutenant gulped. "Sorry, Sir. I'll get right on it."

Six hours later Reeves reported his findings. Mac was in Operations, logging Dr. Goodwin's death into the ship's record.

"Sir? I've finished," Reeves said.

"And?" Mackenzie asked without turning.

"I didn't find anything, Sir. All software checks out."

"Any communications errors?" Mackenzie asked.

"No, Sir. None at all."

Mackenzie turned to face the boy. Reeves squirmed under his captain's gaze.

"I ran a complete software diagnostic on the tube," Reeves continued, "I didn't find a single error. It has to be a mechanical failure."

"I checked the mechanics myself; there was no mechanical failure," Mac said flatly.

"What about tube-death?" Reeves asked. "It's not unheard of, you know."

Mac studied his lieutenant, then finally, "I don't like it, Reeves. I don't like it at all," he sighed. "But it seems to be the only logical explanation, at least for now."

Reeves looked pleased.

"Very well," Mac said. "Go back to your tube. I'll be there shortly to tuck you in bed."

Mac wasn't convinced. Could it be tube death? And why didn't Mother wake him right away?

Mackenzie awoke with a scream to find himself strapped in his tube. Vicky and Cassie were gone -- the nightmares vanquished once more.

His tube was open and with great effort he managed to disconnect himself from the machine. Confusion faded as he returned to life.

He floated from his bed and looked around; once again he was the only one awake.

"Mother? What happened? Why am I awake?"

"THERE HAS BEEN A FATALITY IN POD TWO."

His blood froze. What was happening?

The dead man was in Pod three, tube forty-seven. His eyes were wide open, his mouth frozen in mid-scream, a look of terror etched in the lines of his face. Tubes and wires were ripped from his chest and neck. His fingers were bloodied and bruised. Streaks of blood smeared the inside of the plastic canopy. One thing was certain: This was not tube death.

"Don't bother coming over here, son," Mac called out as Reeves floated into the chamber. "It's pretty ugly."

The boy floated over despite Mac's warning.

"What a mess, Sir," he said flatly

Mac ran a shaky hand through his thin hair.

"I've never lost a passenger, Reeves," he said, staring at the corpse. "Twenty-six years in the service and I've never lost a passenger. And now..."

Silence filled the gloom of the pod.

Reeves remained silent, looking first at his captain, then at the dead man.

"When you eliminate the impossible, whatever remains, however improbable, must be the truth," Mackenzie muttered to himself.

"I'm afraid I don't follow you, Sir," Reeves looked at him quizzically.

Mackenzie looked up at the boy. "That's something a fictional detective, Sherlock Holmes, said."

"What does it mean?" Reeves asked.

"It means that we have a murderer on this ship."

"That's not possible, Sir! Everyone's asleep!"

"It's the only explanation," Mac said. "You can't say this is tube-death. Look at this man!"

"But if it's true, who did it?" Reeves asked. "Someone from the crew? One of the passengers?"

"I don't know," Mackenzie said, bending over the tube. "You know the drill; start a level-three diagnostic on Mother. I'm going to have a closer look at this tube."

The second victim was Dr. David Pickering, Chief Technical Officer. With the loss of Goodwin, and now Pickering, the success of Sagan Four was in serious jeopardy. This had to be stopped if the mission was to have any chance of succeeding.

Mac was deep into his third test of the dead man's tube, his head pounding and his frustration rising, when he remembered something else he read in a Sherlock Holmes story. Something about an unusual incident of a dog that didn't bark in the night.

Why didn't the dog bark? Why had Mother remained silent as two passengers died?

Mackenzie left the pod, a vague idea forming in his brain.

He found Reeves in Operations, hard at work with his diagnostics.

"Report, Lieutenant," Mackenzie said.

Reeves turned from his work. "Same as before, Sir -- everything checks out."

"Very well," Mac said. "Don't waste any more time. Our best bet is to wait 'til we get to Sagan and try to sort things out there. Get back to your tube."

Reeves smiled as he shut down diagnostics.

After Mackenzie sealed Reeves in his tube he returned to Operations and accessed Mother using the same diagnostics Reeves had used.

He ran test after test with nothing to show for it, when he finally found it; a simple, yet unmistakable, error. The diagnostic reported that the file size of one small subroutine had changed since leaving Earth. Reeves should have found it; he had to have seen it.

During the mission, at predetermined intervals, the routine would wake crew members to perform routine maintenance or make flight corrections. It had been modified so that Mother would open a single tube at random intervals, erasing all traces of the event. Mac was not at all surprised to see the tube belonged to Lieutenant Carlton Reeves.

It was so obvious: The dog hadn't barked -- Mother hadn't alerted Mackenzie -- because Reeves was the killer. Reeves had changed the program and Mother she let him: As second in command he was allowed full access to all systems. The only reason Mac had been awakened at all was because Mother performed random checks on all tubes throughout the voyage.

But Mackenzie needed proof, physical evidence. There were no computer records. His only option was to catch Reeves in the act.

Mac quickly added a little subroutine of his own that would wake him if Reeves's tube opened for any reason. When he finished he returned to his tube, leaving Mother to look after the ship.

Mac woke once more. He was alone. Reeves's tube was empty.

Mackenzie quickly unhooked himself. "Mother!" he barked. "Where is Lieutenant Reeves?"

"LIEUTENANT REEVES IS IN POD TWO."

Mac flew to Pod Two. Reeves hadn't activated the pod lighting, but Mac could see a moving beam of light from the lieutenant's flash.

Mackenzie moved silently into the chamber, kicking off from the bulkhead, letting momentum carry him length of the pod, past the transparent coffins of his passengers.

He was less than ten meters from the boy before he stopped. Reeves was absorbed in his work and had no idea his captain was floating in the darkness, watching.

Reeves had an access plate open, his hands deep inside a tube's electronics. Mac could see the tube's display, glowing green and yellow. Relief washed over him when he saw the occupant was still alive.

"Lieutenant Reeves!" Mackenzie's voice echoed off the walls, swirling around the sleepers in their tubes.

Reeves jumped and turned, no more surprised than if he'd heard the voice of God Himself. He raised his flash but Mackenzie had moved behind a tube.

Reeves probed the darkness with his beam. "Captain? Is that you?" He laughed a high, nervous laugh.

"Mother! Lights!" Mac commanded.

The pod was flooded with light. Reeves blinked stupidly at the brightness.

"Mother woke me, Sir," Reeves explained. "There was a malfunction in this tube. I was repairing it, Sir," Reeves's voice cracked.

"Don't lie to me, boy," Mackenzie said. "I found your little program hack. I know you killed Goodwin and Pickering so let's cut the crap, okay?"

Reeves seemed to relax, his face changing as if removing a mask.

"Sure thing, Captain," he said. "So what's next? Are you going to arrest me or something?"

"Yeah," Mac said. "I'm going to arrest you. Does that bother you? Are you going to try to overpower me and escape?"

"Get real, Cap", the boy laughed. "Where would I go? What would I do? It's not like I can just hop off this crate and hitch a ride back home, and I can't fly this thing without you. I knew there was a chance I'd be caught when I volunteered for this mission. It's part of the job."

"Is murder part of the job too?" Mackenzie asked.

"Murder is such an ugly word. I prefer 'assassination'," Reeves said. "This was a political action, not personal."

Mackenzie drew himself closer to the boy. "Who do you work for, Reeves?"

"I suppose there's no harm in telling you," Reeves said. "I work for Earth First. I'm sure you've heard of us."

"Can't say I have," Mackenzie said.

"You must not get out much, Cap," Reeves laughed. "EF is a worldwide organization dedicated to putting the needs of Mother Earth before all others. We don't believe human beings were meant to travel to the stars and we think Sagan Four is a tremendous waste of money and talent. We should spend our money and our energy solving Earth's problems, not playing space cowboy."

"What a load of..." Mac said, "Space is our future, Reeves, our only hope. Your 'Mother Earth' is on the critical list, she's terminal. Where will you go when she's dead? Tell me that, Lieutenant!"

Reeves laughed. "Well, Captain, I wasn't expecting this much energy from you; I was told you were washed up, you know, after your wife and kid croaked."

Mac's face flushed. "What do you know about Victoria and Cassie?"

"I know all about you," Reeves said. "Your wife and little girl died on Earth during the pandemic of '76, didn't they? First your daughter, Cassie, then Victoria. And you weren't there, were you, Captain? You were too busy saving humanity. You didn't have time to be with your wife and daughter. They died alone!"

"Shut up, Reeves!" Mackenzie yelled. "This isn't about me, it's about you! You're under arrest for murder!"

Reeves laughed, full and deep. "You still don't get it, do you? You can take me back to Earth if you want but I'm a hero! I have powerful friends. I won't serve time."

"You're a cocky little twit, Reeves," Mackenzie said.

"I just know how the system works -- I'm connected. Sorry, Captain, but you can't win. Go ahead, do your duty!" Reeves smiled an ugly, hateful smile.

Mackenzie finished hooking the last wire to the boy's body.

"See you when we get back to Earth," Reeves said.

Mackenzie pushed a button and watched the tube canopy close. He bent down so Reeves could hear him through the narrowing opening. "I forgot to tell you," he smiled, "you're not going back to Earth."

The canopy closed with a soft thud and a clink. Reeves squirmed against his harness. Mac punched on the intercom.

"I'm exercising my authority as captain of this vessel," he explained. "We're going on to Sagan and I'm going to leave you there. You're going to spend the rest of your days in space, far, far away from your powerful friends and political connections. Maybe the crew will kill you when I tell them what you did; that's up to them. But I hope they keep you alive, Reeves," he whispered, "for a very long time. Either way, you'll never see Earth again."

He clicked off the intercom, leaving the boy to struggle as the tube slowly put him to sleep.