The Three Doctors (Doctor Who) the Third Doctor (Jon Pertwee) for help when Omega drains their civilisation's power. The serial opened the tenth anniversary year of the series, and features the first three Doctors all appearing in the same serial. This makes it the first "Doctor Who" story in which an earlier incarnation of the Doctor returns to the show. A superluminal signal is sent to Earth, carrying with it an energy blob that seems intent on capturing the Doctor. The homeworld of the Time Lords is also under siege, their power being drained through a black hole. Trapped themselves, and desperate to send help,
K9 (Doctor Who) Jaeger) in the year 5000. K9 subsequently travelled with the Fourth Doctor (Tom Baker) and Leela (Louise Jameson) as a companion of the Doctor in his adventures in time and space until "The Invasion of Time" (1978). In this serial, K9 decides to remain on the Doctor's home planet of Gallifrey with Leela. Immediately afterwards, "Doctor Who" would introduce a second incarnation of K9, played by the same prop; the last scene of "The Invasion of Time" shows the Doctor unpacking a box labeled "K9 Mk II". Although the first incarnation of K9 does not appear again in televised "Doctor