“I am so sorry.”

What did Vitaly mean by that? As the sole American astronaut on the International Space Station, U.S. Air Force colonel Rick Farmer was used to being the target of the Russian crew’s practical jokes. The most recent had involved their sewing him shut inside his sleeping bag and then wide-casting his reaction for the whole net to see.

Now, that had been funny. But this was outside. Different rules when you’re floating outside, only a thin tether keeping you hooked to the station.

The odd thing was that Cosmonaut Vitaly Simakov’s voice had been unaccompanied by his usual booming laugh.

Farmer rechecked his tether, more for mental reassurance than any need. It had been twenty-four minutes since he’d been able to raise Vitaly or anyone else in the station on his suit’s radio. That message was the last Farmer had heard from the mission commander after he’d made his way out of the station to repair the fluky number four solar panel. Even Houston was offline. He chalked up the silence to another one of those technical problems that made daily life in space so difficult, rather than the romance NASA still spun for the media.

With a PhD from Caltech in systems engineering and over four thousand flight hours in everything from T-38 trainers to F-22 stealth fighter jets, Farmer knew that big, complicated things sometimes just did not work as they were supposed to. He remembered the time his twin boys had played around with his flight gear on the eve of his first deployment to Afghanistan, half a lifetime ago. “Daddy needs a helmet because sometimes his job can be really hard.” He hadn’t told them that in his line of work, it was the mundane stuff that was the hardest.

Farmer approached the hatch to reenter the space station.

“Farmer, validate. Open hatch,” he commanded the system.

Nothing.

He said it again, emphasizing each word this time to allow the voice-recognition software to lock on.

“Farmer. Validate. Open. Hatch.”

It was as if the system couldn’t hear him.

He reached for the manual override and lifted the cover that protected the emergency-open button. Well, he thought as he pressed it, this was fast on its way to becoming one.

Nothing.

He pressed again, harder, the force of his fingers against the bright red button pushing him backward in the weightless environment of space. If he hadn’t been tethered to the station, that push would have sent him spinning off at a rate of ten feet per second on a trajectory toward Jupiter.

Nothing. What the hell?

The outside of his visor was gold-coated, the world’s costliest sunglasses. Inside was an array of computer displays projecting everything from his location to the suit’s internal temperature.

Farmer couldn’t help noticing the red light flashing in the corner, as if he needed the computer to inform him that his heart rate was spiking. He paused to center himself with a deep breath, looking down at the sweeping span of blue beneath. He tried to ignore the black void ringing Earth, which seemed to widen menacingly. After half a minute of steady breathing from his core, just like the NASA yoga instructor back in Houston had taught him, he stared hard at the door, willing it to open.

He tried the button again, and then again. Nothing.

He reached down for his HEXPANDO. The expanding-head hexagonal tool had been designed by NASA’s engineers to remove or install socket-head cap screws in hard-to-reach places. It was a glorified wrench.

The instructions explicitly said that the HEXPANDO was “not intended for application of torque.”

Screw it.

Farmer banged the HEXPANDO on the hatch. He couldn’t hear any sound in the vacuum of space, but the pounding might resonate within the station’s artificial atmosphere on the other side of the hatch.

Then a hiss of static and Farmer’s radio came back to life.

“Vitaly, you hear me? I was getting worried there. The comms are on the fritz again, and now the damn voice-command systems on the hatch aren’t working,” said Farmer. “Tell Gennady I am going to send him back to trade school in Siberia. His repair job yesterday actually broke everything. I need you to open manually from the inside.”

“I cannot. It is no longer my decision,” said Vitaly, his voice somber.

“Say again?” said Farmer. The red heart light pulsed just outside his field of vision, as if Mars were suddenly blinking over his shoulder.

“I am no longer authorized to open hatch,” said Vitaly.

“Get Houston, we are going to sort this out,” said Farmer.

“Goodbye, my friend. I am truly sorry. It is orders,” said Vitaly.

“I’ve got an order for you. Open the fucking hatch!” said Farmer.

The soft pulse of static that followed was the last sound Farmer would hear.

After five minutes of pounding on the hatch, Farmer turned from the station to stare down at the Earth beneath his feet. He could make out the Asian landmass wreathed in a white shroud, the cloud of smog stretching from Beijing southward toward Shanghai.

How much time did he have? The red light’s urgent flashing indicated spiking respiration. He tried to calm himself by running calculations in his head of the Earth’s rate of turn, the station’s velocity, and his remaining oxygen. Would it be enough time for the Eastern Seaboard to come into view? His wife and grown boys were vacationing on Cape Cod, and he wanted to look down at them one last time.

Sometimes history is made in the dark.

As he scanned the blackness, Tzu-long thought about what his wife would be doing right now. He couldn’t see her, but he knew that ten kilometers above, Li Fung would be hunched over her keyboard, ritually tightening her ponytail to burn off the tension. He could imagine her rough sneeze, knowing how the cigarette smoke from the other geologists irritated her.

The screens inside the Jiaolong-3 Flood Dragon deep-water submersible were the only portholes that modern science could offer the mission’s chief geologist. His title was truly meaningful in this case. Lo Wei, the Directorate officer sent to monitor them, had command, but ultimately, responsibility for the success or failure of the mission fell on Tzu.

So it was appropriate at this moment, he thought, that he alone was in control, deep below the COMRA (China Ocean Mineral Resources Research and Development Association) deep-sea exploration vessel Xiang Yang Hong 18. This particular pocket of the Mariana Trench belonged to him alone.

Tzu guided the course underwater with a series of gentle tilts of the softly glowing control-sleeve gloves he wore. He was moving too close to the sheer trench walls to consider using the autopilot. He exhaled to clear his mind. There was so much pressure, poised to crush his vessel and everyone’s dreams at any moment.

He adjusted the headset with a nudge of his shoulder. There, just as he thought. Blinking, he leaned forward, as if proximity to the lightly glowing video screen and the crushing darkness beyond the sub’s hull could make the moment any more real.

This dive was the last; it had to be.