A
superluminal signal is sent to Earth, carrying with it an energy blob that seems intent on capturing the Doctor, but has already mysteriously abducted two individuals: a local game warden, and scientific researcher Dr. Tyler. The
homeworld of the
Time Lords is also under siege; they are trapped themselves, with universal energy being drained through a
black hole, threatening to unravel the fabric of time and space. Desperate to send help, the Time Lords break the First Law of Time by recruiting a previous
incarnation of the Doctor from his own past. As the
Second Doctor and the present
Third Doctor cannot cope with each other's personalities, the Time Lords 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. The Doctors investigate, while
UNIT headquarters faces an attack by shapeless lumpy-globule-like creatures. The First Doctor assists both Doctors by correctly surmising that the previously-sent energy blob is a bridge to another universe. The Third Doctor attempts to go alone, but Jo is abruptly abducted with him. The Second Doctor later allows the
TARDIS with himself, the Brigadier, and Benton inside, to be taken by the blob, although this causes UNIT HQ to be stolen as well. Jo, the Third Doctor, and Dr. Tyler, whom they discover there, assess their situation in this new mystery universe of antimatter, inside the black hole. The Third Doctor also deduces that a conversion has taken place for their assailants and themselves to somehow exist in each other's universes without annihilation. Before they can do any more, though, they are accosted by the shapeless creatures and taken to an unfamiliar location. When they arrive, they meet the legendary Time Lord
Omega, who created the
supernova method that powers Time Lord civilisation, but which also supposedly killed him. Omega seeks revenge on the Time Lords, whom he assumes left him stranded alone for centuries in his universe, of which he explains that he willed into existence. Assuming he has been deceived once again by the Time Lords after discovering the Second Doctor and correctly deducing his identity, Omega imprisons both Doctors, Jo, Benton, and Tyler. After the two Doctors help everyone escape through both of their own willpowers, Omega discovers the getaway, and challenges the Third Doctor to a battle of minds, nearly killing him. The Second Doctor convinces Omega to stop, appealing to his desire to escape. Now calmer, Omega explains further to the two that he shaped this reality within the black hole both with his willpower and the power of its
singularity. However, due to this, his will is the only support keeping this reality stable. He cannot freely leave without releasing control, but releasing control would collapse the antimatter universe instantly, annihilating everything in it; and so Omega's intention is for the Doctors to take his place maintaining it. As he prepares to leave with the Doctors' help, they are stunned to find that the extremely prolonged exposure to the singularity has destroyed Omega's physical body; his willpower now also maintains his essence, and he will cease to exist if he leaves. Suffering a nervous breakdown from the shock, Omega now seeks to destroy all creation. Taking advantage of his neurosis, the two Doctors escape back to the TARDIS with all of the abductees. With the First Doctor, the two devise a way to defeat Omega. By accident, the two also discover the Second Doctor's previously-lost
recorder within the TARDIS'
force field generator, and integrate it into their plan. The two meet with Omega again, claiming they can give him his freedom. Omega, though, sharply retorts that he cannot be freed, and demands that they share his exile. The Doctors agree, on the condition that all of his abductees are sent safely back to Earth. Once done, the two present him with the generator. Omega knocks it over in rage at the paltry offer and the recorder falls out; having fallen into the generator during the abduction, the recorder was protected from conversion, remaining as normal matter. The resulting contact annihilates the antimatter universe, creating a new universal source of energy, and ejecting the Doctors in the TARDIS, UNIT HQ, and all of its stolen objects, back to their proper places in the normal universe. With the Time Lords' power restored, they return the First and Second Doctors to their respective time periods. Forlorn, the Third Doctor implies to Jo that death was the only freedom anyone could offer Omega. Out of forgiveness, the Time Lords then send the Doctor a new dematerialisation circuit for the TARDIS and restore his knowledge of how to travel through
space and time, lifting his exile. ==Production==