Monitoring Base XL-7

 was located on a planet owned by the Doctor. Sebastian Musgrove was stationed on the base, alone except for two drones, unaware that the land was actually a sentient being, Telxzana, who was the last of her race and dying. The Fifth Doctor and Nyssa visited the base and helped Telxzana make contact. Sebastian stayed with her until she died, at which time he left the base. (PROSE: Lonely Days)