The story takes place on Christmas Eve in 1900. Jim (played by Thomas Mann) gave a purebred dog named Miss (voiced by Tessa Thompson) to his lover (played by Kiersey Clemons) as a Christmas gift. In this way, Miss gradually grew up in this family full of love and happiness. One day, the hostess found that she was pregnant. The focus of the whole family naturally focused on the unborn baby, which made Miss, who was neglected, feel depressed. Finally one day, Miss, who could not bear it any longer, decided to run away from home. The outside world is not as simple as Miss imagined. Soon, it encountered danger. Fortunately, a stray dog named Chap (voiced by Justin Theroux) reached out to Miss. Under Chap's leadership, Miss felt the joy of freedom for the first time.