In a dystopian Boston, seventeen-year-old Asad lives with his older brother, Tarif, and their grandmother, Gam. Asad, Tarif, and Gram are nightsiders, Black citizens with a gift for seeing the various cracks that open beneath Boston and threaten to swallow the city whole. Nightsiders work to find and seal these cracks during at night while the white daysiders, who cannot sense the cracks, sleep. Tarif mentions the entire city of Louisville is rumored to have disappeared into “total blackout,” swallowed up by cracks that grew too large. Asad fears Tarif has learned this from dangerous online networks.

One night, Tarif leaves work to pursue a girl named Shawna, leaving Asad to fix cracks alone. Sensing a crack nearby from an electric pulse, Asad investigates an area of town not assigned to him. When he finds the crack, its a sort of one-sided mirror Asad can see through to an alternate reality. He sees himself happy, kissing a boy named Avondre.

Haunted by the alternate reality he sees but cannot reach, Asad cannot patch the crack. Gam offers to fix it the next night, but Asad is fearful Gam will discover Asad is queer from the alternate reality it shows. Asad becomes nervous the crack he did not fix will grow so large it swallows the city, similar to what happened in Louisville. Asad joins the underground online network Tarif spoke about and confirms the Louisville rumor. Gam goes to fix the crack.

Longing for Avondre, Asad sees his alternate self with Avondre in other cracks he fixes in the weeks to come. One evening, Asad wakes to find Avondre in his own reality. They introduce themselves.