Timewyrm: Genesys

Gilgamesh, the first hero-king, rules the city o fUruk. An equally legendary figure arrives, in a police telephone box: the TARDIS has brought the Doctor and his companion Ace to witness the first steps of mankind's long progress to the stars. And from somewhere amid those distant points of light an evil sentience has tumbled. To her followers in the city of Kish she is known as Ishtar the goddess; to the Doctor's forebears on ancient Gallifrey she was a mythical terror—the Timewyrm.