In the seventeenth season (1979–80) story "The Horns of Nimon", the fourth incarnation of the Doctor, played by Tom Baker, recognizes the Labyrinth-like building complex that serves as the lair of the Nimons as resembling both physically and functionally a "giant positronic circuit". When adequately fueled, the circuit was capable of transferring massive amounts of energy over vast distances to generate two black holes as gateways to hyperspace and to sustain a tunnel that served as the motive power between them for the transport of an invading force of Nimons from the dying planet Crinoth to Skonnos.