Hours after a young man walked into Marjory Stoneman Douglas High School on February 14 with an AR-15 rifle, a black duffel bag, and backpack loaded with magazine cartridges, Jaclyn Corin took it upon herself to share the enormity of her experience in the way she knew how. She had spent over three hours captive in the school, and had once even tutored the young man who took 17 peoples’ lives that day. Shortly after staggering home, she turned to social media, where friends were sharing intimate accounts of their horror. Within hours, the #NeverAgain hashtag had become a global phenomenon. “Please pray for my school,” Corin began her Facebook and Instagram posts. She worked up toward a passionate call for strict gun regulation. “We NEED to work together to bring change,” she concluded. “MAKE IT STOP.”

Corin, 17, is a petite blonde young woman with fair skin, flowing hair, and a soprano voice that doesn’t carry in crowds. But she has a presence. She is junior class president at M.S.D. and was previously vice president her freshman year. The commitment forced her to give up dance class after 13 rapturous years. (“Dance was my life and my love,” she said.) Weeks before the shooting, she was planning a nursing career. But an urgency awakened in her that afternoon. Corin would soon learn that her friend Cameron Kasky was in the early stages of planning a march on Washington to take place in March. Corin feared, however, that the undertaking would require weeks of planning and organization, and that the Douglas story would subsequently fade into the background. “The news forgets,” she recalled to me recently. “Very quickly. And if we were all talk and no action, people wouldn’t take us as seriously. We needed a critical mass event.”

Corin began to realize her wish the next day. A family friend forwarded her Facebook post to Rep. Debbie Wasserman Schultz, the former chair of the Democratic National Committee, who met her at a vigil, and connected Corin to her state senator, Lauren Book, soon thereafter. Corin began to conjure a vision for striking fast while the story remained in the news cycle, and agitating for meaningful legislative change: she pictured waves of students from multiple schools descending on the state capitol in Tallahassee. But the organizational hurdles appeared overwhelming. And it would take way too long. So she settled on a lightning strike. Corin would recruit a couple hundred students from M.S.D., bus them eight hours to Tallahassee on Tuesday and help them lobby for new gun laws. Book signaled that she was ready to help make it happen.

Corin was beginning to map it out Friday night, when Kasky called at 9:30, past her normal bedtime. The two friends had weathered the attack together. Kasky had just swung by her classroom to pick up his autistic brother, Holden. After hours in lockdown, the SWAT team suddenly busted in, shattering the glass in the door. Five hulking men barked orders and pointed assault weapons. It was terrifying, Corin recalled, but she was most afraid for some of the autistic kids who didn’t comprehend and were not complying. “If they had made a wrong move, who knows,” Corin said.