The One and Only Family by Katherine Applegate is the fourth installment in the One and Only series about a gorilla named Ivan who lives in a zoo park. The book brings in characters from the first three novels while focusing on Ivan becoming a father, the challenges he faces being both a parent and the leader of his troop, and his relationship with the humans who care for him.

The One and Only Family was an instant #1 New York Times and Indie Bestseller, and the entire series has achieved best-selling status, with The One and Only Ivan (2012) also winning the Newbery Medal. Applegate has penned several New York Times best-selling novels for young readers, including Willodeen (2021) and Wishtree (2017), which won the Christopher Medal and the Golden Kite Award, among others. She began her career ghostwriting books in the Sweet Valley series before transitioning to her own works, mainly middle grade science fiction and fantasy. In partnership with her husband, Michael Grant, she also co-wrote the popular Animorphs series. Currently, she lives in California.

This guide refers to the 2024 Harper Collins digital edition.

Content Warning: The source text and this guide refer to animal cruelty and discuss trauma.

Plot Summary

The One and Only Family returns to the perspective of Ivan the gorilla for the final installment in the series. At the book’s outset, Ivan informs the reader that he is about to become a dad. He starts the narrative shortly before he and his mate realize that they will soon be parents. Through turns both witty and serious, Ivan recounts how he and his mate had missed the signs of pregnancy, passing an expanding stomach off as eating too many mangos. Ivan also details the role that their human caretakers play in the process, including leaving baby gorilla dolls as a clue. Still, Ivan only officially learns the truth when the vet examines his mate.

Ivan convinces himself that parenting can’t be too difficult because other parents make it look easy. Ivan and his mate are surprised when she delivers twins; this brings back memories of Ivan’s time in the wild because he, too, was a twin.

The moment Ivan sees his children, a protective instinct like he’s never known comes to life inside him. In addition to his role as silverback leader of his troop, Ivan takes on the most important job of his life—keeping his children safe.

Dealing with newborns turns out not to be too difficult. However, by the time the twins are two years old, Ivan concludes that he was very wrong that parenthood was easy. Ivan finds it difficult to answer the twins’ endless questions about him without digging into his past. Ivan lost his family to poachers when he was very young. Afterward, he was kept in a human home for years before being held captive in an arcade zoo where he was treated poorly. The best things to come out of that time were Ivan’s best friends, Bob (a dog) and Ruby (an elephant), who he still sees frequently. Both counsel Ivan not to hide his past from his children because it is part of who he is, but Ivan still can’t bring himself to tell them.

Shortly after the twins are born, a documentary is made about Ivan and his family. The night the film is scheduled to be shown at the zoo, a younger male in Ivan’s troop approaches Ivan to offer his best for the viewing. This male also lost his family to poachers, and Ivan accepts his good wishes for what they are—the understanding that both their lives have been irrevocably changed. When the documentary plays, Ivan is shocked to find that it isn’t about the twins. Rather, it shows his painful past. Feeling ashamed and embarrassed, Ivan runs away.

Ivan doesn’t realize that one of his children followed him until he finds her being held by a human boy who fell into the gorilla enclosure. Mistaking the boy as a threat, the younger male whom Ivan had spoken with earlier grabs the child. Humans flood the scene, and one man is poised with a gun, ready to shoot the young male gorilla. After seeing the documentary, Ivan realizes that his past isn’t something to be ashamed of. Rather, it lets him be a compassionate leader of his troop. He gets the younger male to back down. The human boy is rescued, and Ivan’s daughter returns to her family. Afterward, Ivan promises to answer questions about his past honestly, realizing that it is part of who he is.