Most twists come at the end. Not so in We Are All Completely Beside Ourselves, where the big reveal happens on page 77, a little under a quarter of the way through. I could review the novel without giving this reveal away. I could ramp up its universal themes and praise, vaguely, Karen Joy Fowler’s handling of family secrets, sibling rivalry and the unreliability of memory, all of which she treats with the same wry insight she brought to loneliness and friendship in The Jane Austen Book Club. But to write about We Are All Completely Beside Ourselves in this way would be to ignore what separates it from a hundred other wryly insightful novels and what explains its place as one of the two American novels on the Booker shortlist; both its singularity and the singularity of the relationship between Rosemary, Fowler’s narrator, and her sister, Fern, who disappeared when Rosemary was five years old.

So here it is (stop reading now if you’d rather not know): Fern is a chimpanzee. Almost exactly the same age as Rosemary, she was raised as far as possible in the same way. (Their father planned to name the babies after their two grandmothers and was astonished when each