Ebony And Ivory — Sue Perkins

A deadly plague attacks the Eos, forcing Robard and Tazia to put aside the intimacy problems in their arranged marriage. Robard organises the Dukes of Hejmen to assist in the crisis. Meanwhile Tazia becomes the telepathic holder of the Eos history and hears rumours of a lost tribe of the spirits. Their only hope of discovering a cure is to find these spirits. Failure means the extinction of both the Eos and humans.