Are there more worlds beyond Pluto? What might such a world be like? Planet Nine tells a tale of the search for another world hidden in the darkness. Planet Nine follows planetary scientist/explorer Mike Brown and his team at CalTech as they uncover new worlds such as the remarkably bright Eris; tumbling Haumea, an egg-shaped object rotating incredibly fast; and Sedna, whose orbit takes it deep into the far reaches of the Solar System. Is there a new planet beyond even these distant objects?