The Haldenmor Fugue (short story)

Summary
The Doctor lands in a major city in Eastern England in the year 2180. Problem is, the Doctor strangely does not recognize the city. Soon, he finds himself partnered with a strong-willed security guard named Carla, investigating odd happenings in a building where "ghosts" are being reported attacking customers. The Doctor soon realizes these "ghosts" are in fact Vikings who settled in the area back in the 10th century, but who are interacting with the 22nd century via a rift in time created by a time travel experiment gone haywire. But in order to put things right, the Doctor must not only close the rift, but doing so will make it so the city of Haldenmor, and possibly his new friend, Carla, never existed.

Characters

 * The Doctor
 * Has taken to talking to himself because of his lack of companionship.
 * Regrets that he is unable to take Carla on as a companion.
 * Carla
 * In the Haldenmor timeline, is a security guard for a major building.
 * In the proper timeline, is a jet pilot named Yarah.

Continuity

 * The Tenth Doctor spends literally years tracking down Carla's whereabouts after having repaired the timeline.