For thirteen years, Ben Tomlin was an only child. But all that changes when his mother brings home his new 'baby brother' Zan, an eight-day-old chimpanzee. Ben's father, a renowned behavioral scientist, has uprooted the family to pursue his latest research project: a high-profile experiment to determine whether chimpanzees can acquire advanced language skills. Ben's parents tell him to treat Zan like a little brother. Ben reluctantly agrees.

In 1973, when a renowned Canadian behavioral psychologist pursues his latest research project--an experiment to determine whether chimpanzees can acquire advanced language skills--he brings home a baby chimp named Zan and asks his thirteen-year-old son to treat Zan like a little brother.