The following version of this book was used to create this guide: Keller, Tae. When You Trap a Tiger. Penguin Random House, 2020.

In Chapters 1 - 9 Lily Reeves, her sister Sam, and her mother Joan arrive in Sunbeam, Washington, where they are to live with Joan's mother, Halmoni. Lily sees a tiger in the middle of the road on their way there but refrains from telling her family, since they are too busy arguing and she knows no one but Halmoni will believe in a magical tiger. When she tells Halmoni about the tiger, Lily's grandmother believes her and says she thinks the tiger is there to get stories back that Halmoni stole a long time ago. Lily sees her grandmother vomiting and realizes Halmoni is likely quite ill.

In Chapters 10 - 18, Lily meets Joe and Jensen -- staff members at the library across the street from Halmoni's house. She also meets Ricky, a chatty boy around her age who professes to know about tiger traps. Lily recruits his help in building a tiger trap which she hopes will lure the tiger to her and help return the stories to her which she thinks are stores in some jars Halmoni keeps in her basement.

In Chapters 19 - 27, Lily and Ricky's trap works -- the tiger gets caught one night when Lily sneaks back down to the basement. Lily agrees to return stories to the tiger and listen to them carefully in exchange for the tiger to help Halmoni with the brain cancer she is suffering from. The first story tells of a girl that is half-human and half-tiger but wants to hide the part of her that is a tiger. The next day, a family trip to the restaurant is cut short because Halmoni's illness causes her to lose her memory and begin rambling and harassing restaurant patrons. That night, Lily listens to the next story in which the tiger-girl from the last story is now a grandmother struggling to accept her granddaughter's 'two skins,' just as she struggled to accept her own earlier.

In Chapters 28 - 36, Lily and Sam run to the library after Halmoni once more loses her memory and yells at them. There, Ricky and his friends welcome Lily but quickly begin to gossip about her grandmother. In retaliation, Lily brings Ricky a pudding cup full of mud. She gets into trouble at home but bonds with her mother when she explains her reasoning and hears how her mother struggled to accept that change happens and is inevitable. Lily becomes more used to the idea that her relationship with Halmoni might be changing forever but that that is not necessarily a tragedy, merely an inevitability. Lily apologizes to Ricky and the pair are fast friends again. At home, Lily speaks to Halmoni about her illness but is shocked to hear that Halmoni is resigned to die. In a fit of anger, she runs to her room and breaks the story jars.

In Chapters 37 - 46, Halmoni runs to Lily and Sam's room to see what is wrong and collapses. When their mother takes Halmoni to the hospital, Sam and Lily decide to follow. Sam drives them to the hospital and Lily and her bond over their grief. At the hospital, Lily sees the tiger who confesses that helping Halmoni does not involve a 'forever' cure, but rather an emotional healing which unleashing those stories has achieved. Halmoni tells Lily that she finally feels at peace and passes away. The family grieve by making rice cakes together afterwards. Sam assures Lily that, just like when their father died, the memory of Halmoni will stay with them forever but the pain will recede.