Arkheon, also known as the Planet of Ghosts, was a planet located near the Crab Nebula, just past the Pleiades, left at the Blue Star Worlds. Temporal echoes resembling ghosts roamed the surface due to the Arkheon Threshold, a time rift in the core. The world was virtually destroyed by the Daleks.
During the First Dalek Incursion of the Second Dalek War, Arkheon was hit by a "Planet-splitter" missile. The missile strike destroyed half of the planet, exposing the core. The fallout killed most of the Arkheonite inhabitants. The survivors eventually mutated into mindless, savage beasts.
Forty years later, the Doctor and the crew of the Wayfarer discovered that the Daleks had turned the area around the core into a slave labour mine using the colonists who evacuated Auros in an attempt to locate the Threshold and use it to become masters of time. They also used the base for experimentation. The group was captured by the Daleks and the Doctor admitted who he was. He was tortured by Dalek X before being given a tour of the base. The Doctor defeated the Daleks, and Earth Command sent in forces that destroyed the remaining Daleks and freed the prisoners, and the Doctor sealed the Threshold, so the Daleks could not exploit it. (PROSE: Prisoner of the Daleks)