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,
The Doctor (Doctor Who) that time was that regeneration had turned back the Doctor's clock, making him younger both in appearance and in biological age. Since the Doctor's age had never previously been given, 450 Earth years became a starting point onto which further years would be progressively added as the series continued and the character lived out his further incarnations. The Third Doctor implied in "Doctor Who and the Silurians" (1970) and in "The Mind of Evil" (1971) that he had a lifetime that covered "several thousand years". While the Doctor's age has never been a known quantity, these numbers are the most