In order to get closer to the sister she never really knew, Agnes embarks on her own adventure with the help of Dungeon Master Chuck to play the game as Tilly designed.

As she delves deeper into her quest, the fantasy world and reality begin to collide and mix as Agnes searches to connect with Tilly and realizes how much of her sister she never knew.

[1] Nguyen intentionally wrote the characters in a way that allowed for actors of any race to be cast into every role, "We wanted to see the diversity you would find on the New York subway onstage.

[6] Following a 2013 award by the American Alliance for Theater and Education, the play has, as of July 2020[update], been staged close to 800 times, mostly by high schools and colleges.

Changes include depicting the climactic battle through dice-rolling rather than a physical fight, as well as setting the entire play in 2020 and updating its pop culture references accordingly.

[13] In She Kills Monsters, Agnes discovers Tilly was a lesbian and used her Dungeons & Dragons campaign as an outlet for her struggles of being out in school, yet "in the closet" with her family.