A pretty blonde woman waited for an express train on the crowded subway platform, fiddling with the top button of her coat.

Beside her, a Puerto Rican man in a suit frowned at his cellphone. Two young mothers with babies strapped to their chests talked about the pros and cons of swaddling above the roar of the arriving train.

The doors opened and the blonde woman rode for five stops, waiting until the crowd packed the subway car. Crammed between a chubby kid and a heavyset woman, she took a knife from her bag. A chef’s knife, ten inches long, a wedding present from a college friend. She remembered unwrapping the box.

A wiry old man beside her was holding onto the strap and swaying. The blonde pushed the knife into his side, just below the rib cage. The man slumped but didn’t cry out, and she took the knife from his side and stabbed the heavyset women in the small of her back.

The man made a gasping noise and the heavyset woman jerked and the blonde pulled at the knife. It stuck, so she pulled harder. Blood covered her hand. The heat surprised her.

Then the woman screamed and the old man collapsed and the blonde opened a chubby Asian kid’s arm. The crowd surged around her in a panic. Blood splattered the floor and slaughterhouse screams echoed in the cramped frenzy.

She slashed at a terrified businessman and finally found her voice. "Stop me," she gasped. "Oh, God, please--make me stop."

Someone tackled her from behind and knocked her down. The subway rang with screams. She felt her slick fingers scrabbling inside her bulky peacoat. She curled on the floor as the blows rained down.

The subway rumbled beneath her, and she trigged the explosive vest.