Milo, who lives in Brooklyn with his two moms, and Hollis, who lives in Minnesota with her mom Leigh (her other mom Pam passed away seven years earlier)—who were both conceived via in vitro fertilization using the same anonymous sperm donor. When Milo’s doctor suggests that his biological father undergo genetic testing to help diagnose his severe allergies, Milo reaches out to Hollis, whom he met once as a young child before Pam’s death, to help him search for Donor #9677. Though initially reluctant, Hollis is encouraged by her mother, who is newly energized by the possibility of reconnecting with Hollis’s half-brother. In the process of their search, Milo and Hollis locate three additional donor siblings, and together with Milo’s best friend JJ (who is adopted), they embark on an engaging adventure to find their biological father while discovering the true meaning of the “other F-word”: family. The novel, told in alternating third-person narratives, explores themes of identity, belonging, same-sex parenthood, grief, and what family truly means, celebrating the bonds that emerge between these newfound siblings while depicting their mixed feelings about their complicated yet loving families.