Meet the Cooke family: Mother and Dad, brother Lowell, sister Fern, and our narrator, Rosemary, who begins her story in the middle. She has her reasons. I spent the first eighteen years of my life defined by this one fact: that 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.