When two bombs went off near the finish line of the Boston Marathon in 2013, clouds of smoke appeared and then dissipated, revealing streets packed with terrified runners, spectators, and families. The aftermath left urgent questions: Who did this? How did they do it? For what reason? The internet (incorrectly) identified the perpetrator. The manhunt for the real bombers lasted days. Internet indoctrination and homegrown terrorism were top concerns. While HBO's new documentary Marathon: The Patriots Day Bombing certainly takes advantage of this dramatic material, the film surprisingly spends a good deal of time exploring the gradual recovery of people who lost limbs in the attack.

Directors Ricki Stern and Anne Sundberg (who have made general-interest documentaries about topics spanning from Joan Rivers to UFOs) focus on stories of rehabilitation paired with nerve-racking footage and commentary from the bloody search for the Tsarnaev brothers. Relying heavily on retrospective interviews, home videos, archival footage, and fair use clips, they reconstruct the story beginning the morning of the marathon. While the fast-paced pursuit adds a level of suspense, the directors' main interest is the survivors' slow physical progress and enduring trauma, and they make a real effort to avoid glamorizing the perpetrators.

All of this, while admirable, sounds deeply depressing—but ultimately Marathon is a kind of feel-good movie. Moments of levity range from adorable service-dog videos to wry jokes about missing legs. We learn that for the most part, strangers are kind, Boston's spirit survived the ordeal unbroken, and victims became close friends. One of the sweetest moments comes toward the end when former long-distance runner Jessica (who faced, and continues to face, an incredibly tough recovery) makes an introduction while standing near the finish line of the Boston Marathon, years after the event that cost her the life she used to know. "This is Celeste," she says, smiling. "She's another friend from the marathon bombing."

Marathon will make its wide debut on November 21 on HBO.