Douglas students returned to class two weeks after the shooting, on February 28, but on the Sunday prior, the school held an open house. In one of the book’s more heartbreaking scenes, Cullen notes how painful and scary the first reunion between students and their terrorized school can be. The high school that Sunday still felt, in some ways, like a crime scene: Helicopters hovered, capturing video of the school for TV news, and the sound of the chopper triggered anxiety and panic for some of the students who had heard the motors over their school the day of the shooting. One student notes that walking around that day, he and his friends heard a car engine go pop pop pop, “and we all started hyperventilating.”

When classes did resume, though, Cullen describes a school transformed into something more like a rehab center. Classes weren’t really classes at first: “So much Play-Doh, so many comfort dogs,” one student, Daniel Duff, says. (The Play-Doh he found somewhat ridiculous; the comfort dogs he found wonderful.) Another student, Lauren Hogg, describes coming back to school to find “therapists literally everywhere,” even in the school library. Their on-call availability, she says, was immensely helpful for students who were experiencing grief that came in waves, washing over them at unpredictable and sometimes inopportune moments.

Read: The developing norms for reopening schools after shootings

The weeks that follow a school shooting, Cullen writes, are shaky. Students’ routines resume, and many find comfort in the returning familiarity and controllability of their days, but many still experience sudden moments of fear, worry, and sadness at school. When Matt Deitsch, the older brother of two of the survivors, tells Cullen about his little sister’s accounts of being at Douglas after the shooting, he says she’s one of many students who get anxious when they use the bathrooms. “She says, ‘Now when I go to the bathroom I think if I take a little longer to wash my hands maybe I’ll survive if it happens again,’ ” Deitsch says. Or sometimes she’ll take the long way back from lunch and wonder if this choice will save her life.

Many of the students Cullen spoke with mention the never-quite-normal presence of empty desks where students killed in the shooting used to sit. One student says sitting next to a slain friend’s empty desk in classes they used to share is “when it hits [him] the worst.” Another finds it haunting that during other periods of the day, “people probably sit there [in the conspicuously empty desk] and they have no idea this desk is the one we all look at in our class.”