It had been a massive labyrinthine network of long, interconnected tunnels that were dark and drafty. There were cameras everywhere. She’d passed thick glass windows revealing chambers that looked like scientific labs, clean and brightly lit. The Mogadorians inside had worn white plastic suits and goggles, but she’d raced by so swiftly she couldn’t tell what they were doing. A sprawling room housed a thousand or so computer screens with a Mogadorian sitting in front of each, and Six assumed they were looking for signs of us. Just like Henri, I thought. One tunnel was lined with heavy steel doors she had been sure held other prisoners. But she sped on, knowing her Legacy was far from developed and terrified she wouldn’t stay invisible for very long. The siren had continued to wail. And then she reached the heart of the mountain, a great, cavernous hall a half mile wide and so dark and murky she could hardly see to its other side.

The air had been stifling and Six was already sweating. The walls and ceiling were lined with huge wooden trellises to keep the cave from collapsing, and narrow ledges chiseled into the rock face connected the tunnels dotting the dark walls. Above her, several long arches had been carved from the mountain itself to bridge the great divide from one side to the other.

She had pressed herself against a rocky crag, her eyes darting back and forth for a way out. The number of passageways had been endless. She’d stood there overwhelmed, her eyes sweeping across the hollow darkness, seeing nothing at all that looked promising. But then she did—far across the ravine, a pale pinprick of natural light at the end of a wider tunnel. Just before she climbed the wooden trellis to reach the stone bridge that led to it, something else caught her eye: the Mogadorian who had killed Katarina. She couldn’t let him get away. She followed him.

He entered the room where he had killed Katarina.

“I went straight to his desk and took the sharpest razor I saw, then grabbed him from behind and slit his throat. And as I watched the blood gush and spread across the floor, followed by him bursting into ash, I found myself wishing that it would have been possible to kill him a little more slowly. Or to kill him again.”

“What did you do when you finally got out?” I ask.