I was in a trance as Villaverde led me to his desk, which held a huge computer screen. Before I knew it, I was watching grainy black-and-white footage of Caro. She wore a fitted dark top and leggings, and her blonde mane was pulled back in a ponytail. I watched her jog up to an empty intersection and pause, pressing her hand against the center of her chest.

It was like a horror movie, only I knew exactly how this one ended.

“The one thing that was a little funny was that your sister went running down to the United Nations,” Villaverde said. “Her nanny said she liked to run in Central Park. Any idea why she went south instead?”

“No,” I whispered, my eyes transfixed by the screen.

I watched Caro run, her calm face oddly pained. Had she known she was going to die?

“This is the bad part, at the Isaiah Wall,” Villaverde said.

Caro clutched her chest and paused, but she slowly made her way up the steps, then vanished.

I stared, barely blinking, waiting for more.

“Where did she go?”

“The steps curve up. There’s a blind spot after that landing,” Villaverde said. “She’ll be on screen again in a sec. I can fast-forward . . .”

“No.” I wanted him to leave it. As the seconds ticked by, sweat dribbled down the back of my neck. There was Caro, straightening up at the top of the stairs, rolling her neck from side to side. She took four steps and vanished again. The next camera that caught her was farther away. My sister stepped through a waist-high gate and disappeared.

“Where did she go?” I demanded.

“Into the park. There are no cameras in there. But no one else goes in or comes out while she’s there.” He fast-forwarded. “There’s five minutes of nothing. Then this.”

Finally my sister reappeared, only she was moving very slowly, hunched over like she’d aged seventy years. Her left hand was on her chest, and her right was touching the back of her head. She faded off camera again and materialized at the top of the steps beside the Isaiah Wall. Suddenly, both hands went to her heart, and she convulsed. Her body made a graceful little quarter-turn and she dropped, disappearing from the camera’s view until her body fell onto the stone landing. Even though there was no sound on the video, I could hear a sickening thud.

“You saw her clutching her chest?” Villaverde asked. “She was already in cardiac arrest then. That’s why she fell.”

“Why was she touching her head?”

“Dizziness from her heart, probably.”

“Did she have a head wound?”

“I told you she got a concussion,” he said. “You saw her fall. She hit those steps hard.”