Kappa 12

 was a sentient anomaly from a universe different from the Doctor's. It had psychic abilities. It had no physical presence in the Doctor's universe but could warp space/time.

Kappa 12 took over employees of the King and Empire Railway Company. It created rail lines that linked railway stations via singularities. Its actions would have resulted in the Earth's destruction within twenty-three months, but it was stopped by the Fourth Doctor, with the aid of a King and Empire employee named Nicholas Clement, who was able to partially resist Kappa 12's psychic control. (PROSE: The Northern Heights)