Narrator, Rosemary Cook, begins her story in the middle. "I spent the first eighteen years of my life defined by this one fact: I was raised with a chimpanzee," she tells us. "It's never going to be the first thing I share with someone. I tell you Fern was a chimp and already you aren't thinking of her as my sister. But until Fern's expulsion, I'd scarcely known a moment alone. She was my twin, my funhouse mirror, my whirlwind other half, and I loved her as a sister." Rosemary was not yet six when Fern was removed. Over the years, she's managed to block a lot of memories. She's smart, vulnerable, innocent, and culpable. With some guile, she guides us through the darkness, penetrating secrets and unearthing memories, leading us deeper into the mystery she has dangled before us from the start. Stripping off the protective masks that have hidden truths too painful to acknowledge, in the end, "Rosemary" truly is for remembrance.

Coming of age in middle America, eighteen-year-old Rosemary evaluates how her entire youth was defined by the presence and forced removal of an endearing chimpanzee who was secretly regarded as a family member and who Rosemary loved as a sister.