An Old Friend

An Old Friend is the fourth episode of the eleventh series of Doctor Who. It is significant for being the first time in the revived series, and the first time since 1981's  Warriors Gate that the character of Romana makes a return to Doctor Who. The fourth incarnation of Romana, who survived the Time War, helps the Doctor and Renee to stop another Old God, Nagurith, on the ancient world of Sagoth's Orb from enslaving the native Sagoths.

Synopsis
Tracking another Old God to Sagoth's Orb, the Doctor and Renee find that Nagurith, god of enslavement and subjugation, has enthralled the native Sagoths. But someone else is on Sagoth's Orb, a person the Doctor thought was long dead...