Doctor Who Classic: The Three Doctors Episode 1

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 Time Lords do the unthinkable, breaking the First Law of Time by recruiting a previous incarnation of the Doctor from his own past. As the Second Doctor cannot get along with the present Third Doctor, they attempt to retrieve the First Doctor to "keep them in order", but he is trapped in a "time eddy", unable to fully materialise, communicating through a viewscreen.