Tumble follows 12-year-old Addie as she finds and meets her biological father and extended family members. The action in the book is instigated by Addie’s mother Lourdes and stepfather Alex when they present the idea of Alex adopting her. Addie insists that she meet her biological father first, whom she knows nothing about, before she decides. On her journey of self-discovery, Addie demonstrates how important family is and how it impacts one’s identity.

An added impetus for Addie to look for her father is that Lourdes is pregnant with Addie’s half-sibling, who will be arriving soon. With Addie’s immediate family growing, and in addition to the potential adoption, she naturally has questions about her own biological father. The idea of nature versus nurture is presented through Addie’s reflections: She has been raised by Lourdes for all her life, and by Alex for a good part of it. However, she cannot ignore the fact that half of her genetic makeup comes from a complete stranger, and she has questions about which parts of who she is are informed by her father.

Thus, Addie goes searching for Manny, and when she finds him, there are some undeniable similarities. Besides a physical resemblance, she learns that they have similar tastes and preferences, and over time she also discovers that she shares the same thrill for the stage as Manny and the rest of her paternal family.