Sixteen-year-old Sid barely remembers his birth mother and has no idea who his father was. Raised on an idyllic island by loving foster parents, Sid would be content to stay there forever, drawing, riding his bike, hanging out with his friend Chloe and helping out with Fariza, a newly arrived foster child. But when a stranger named Phil arrives on the island with disturbing news about his birth family—including a troubled younger brother—Sid leaves all that is familiar to help find the sibling he didn't know existed.

What he discovers is a family fractured by mental illness, but also united by strong bonds of love and compassion. As Sid searches for his brother, gets to know his grandmother, and worries about meeting his biological mother, he realizes that there will never be a simple answer to the question, Am I my brother's keeper?