Dr. Hugo Archibald, a physician, frequently brings home a variety of exotic animals. His latest addition is a chimpanzee named Jennie. Dr. Archibald is often absent, leaving his son Andrew feeling neglected. Meanwhile, his wife Lea is not fond of Jennie, believing she causes problems. However, the children quickly grow attached to her. Jennie stands out because she is learning sign language, becoming an integral part of the Archibald family. Andrew, in particular, forms a strong bond with Jennie, who shares his interests in baseball and comic books. She also provides support to Andrew during conflicts with his father. Dr. Pamela Prentiss begins working with Jennie, but she disapproves of the care Jennie receives and comes across as impolite to the Archibalds. Although Dr. Prentiss attempts to teach Jennie sign language in a way that confuses her, Lea discovers a method that Jennie comprehends.