Behind me, I heard the metal gate in the vault room rattle violently.

“Clara!” a voice roared from above. “Stop running!”

I didn’t look back.

At the bottom of the stairs, I found myself in a long corridor filled with heating pipes.

A sign on the wall pointed toward the subway transit connection.

Many of the older buildings in downtown Boston had direct basement access to the T.

I pushed through another heavy door and ran onto a tiled walkway.

The air was thick with the scent of subterranean moisture.

I was back in the subway system, but in a different tunnel.

I cradled the twins tightly against my chest, shielding their heads with my hands.

Luca began to cry, his high-pitched wails bouncing off the tiled walls.

“Shh, baby, please,” I whispered, keeping my pace.

I could hear heavy footsteps running behind me.

There were at least three of them.

I turned a sharp corner into a pedestrian underpass.

A train was rumbling on the tracks below, the vibration shaking the ground beneath my feet.

I ran down a set of steep concrete stairs toward the outbound platform.