The Doctor and the Master follow the Monitor to the central register, where he's trying to salvage the CVE work. Tegan follows.
The Monitor tries to use the antenna to broadcast a permanent solution to the nearest CVE. The Master proposes using their TARDISs to salvage as much of the Universe as they can. But their plans are abandoned when the entropy kills the Monitor and the Master runs in fear.
The Doctor and Tegan pull apart the Monitor's computer, which has the intact CVE program. He decides to return to Earth, where there will be a computer than can run the program.
The Watcher takes the TARDIS out of time and space.
The Doctor frees the Master, who is trapped by rubble. They take his TARDIS back to the Pharos control room on Earth. The Doctor knocks out the technician to save him from being killed by the Master.
Adric meets with the Watcher in the cloister room. He tells Nyssa that the Watcher knows what is going to happen. He returns to the console room to take the TARDIS to the Pharos project. As he sets the controls, they watch entropy expanding out and destroying more of the Universe. Nyssa watches in horror as Traken is destroyed. Adric then returns to Earth.
With the program installed, the Doctor and the Master will have to install a lightspeed overdrive in the antenna. They are spotted by guards. Tegan, Adric and Nyssa turn themselves in to allow the Doctor and the Master to proceed. The Doctor goes to the antenna but the Master returns to the control room for his eliminator and TARDIS.
They point the antenna at the CVE and install the overdrive. The Master leaves the Doctor to broadcast the program while he records an extortion message to be broadcast to the Universe. With the CVE under the antenna's control, he can threaten them with annihilation.
The Doctor leaves to break the antenna cable, thus leaving the CVE permanently stable. The Master moves the dish to try to make the Doctor fall. The Doctor crawls across the gantry and yanks at the cable. Only with his weight does it come loose, but he is left dangling hundreds of feet in the air.
Visions of his old enemies appear before him and his grip on the cable slips. He plunges to his doom.
As the Master escapes, Adric, Nyssa and Tegan approach the Doctor's crumpled form. They call out to him and he has visions of his past companions. He wakes and tells them, "It's the end, but the moment has been prepared for."
The Watcher appears and merges with the Doctor. The Time Lords glows and regenerates, taking the form of a young blond-haired man.