The TARDIS lands on the Shadow’s planet and the Shadow sends K-9, now under his control, to watch over the Doctor and report back to him. In the TARDIS, Romana warns that they can’t find the sixth segment without the Tracer, which is being used to hold the sixth artificial segment in with the others. Astra wants to stay in the TARDIS, insisting her destiny no longer lies on Atrios. However, the Shadow speaks to her telepathically, telling her to bring Romana to him. The Doctor realizes something is going on and plays along. As they leave, the Doctor picks up a galactic distress signal.
Astra takes Romana into the corridors and the Shadow orders K-9 to follow the Doctor. The Doctor emerges with a tracking device and comes face to face with images of Romana and Astra. They disappears and the Doctor realizes that the Shadow is trying to separate them. He proceeds onward, following the signal, and the Shadow sends multiple images of Romana. He then finds images of himself used as a distraction. The Doctor boasts that he realized that Astra is under the Shadow’s control. The Shadow, unimpressed, declares that he serves the Black Guardian and sends the Doctor plummeting into oblivion.
Astra takes Romana to the Shadow’s chamber and a mute take her prisoner.
The Doctor recovers consciousness and finds the distress beacon nearby. A hidden panel opens a man wearing a technician’s uniform emerges. The man recognizes the Doctor, calling him Thete: “Theta Sigma.” He introduces himself as Drax from the Class of ’92, 450 years ago. The Doctor realizes who he is. Drax admits that he failed out and went into maintenance all over the galaxy. He admits that he designed Mentalis and was unaware that he was working for the Shadow. He built the distress beacon and tried to summon help. Drax admits he hasn’t been able to find the transmat shaft and his TARDIS is back on Zeos. He takes the Doctor back through the panel to his workshop. The Doctor sees his dimensional stabilizer, and Drax claims he’s been there for five years. The Doctor notes that he should have easily been able to escape using the stabilizer and wants to know what Drax is up to. However, the Doctor figures that Drax plans to get the Doctor to take him to the TARDIS, knock him out, and get the Key of Time. The Doctor appeals to Drax’s class sentiment to work with him against the Shadow.
Romana collapse from the Shadow’s torture after telling him everything she knows. It’s not enough to let the Shadow to get the Key of Time. The Shadow sends K-9 to find the Doctor.
The Doctor and Drax work on Drax’s dimensional stabilizer. Bored, the Doctor finally crawls out a tunnel and finds K-9. K-9 addresses him as “Doctor” and the Doctor realizes something is wrong. He tries to pull the control box off but K-9 pulls away, and then informs the Doctor that the Shadow wants to exchange Romana for the Key of Time. The Doctor says he’ll give it serious consideration, and then manages to grab K-9 and shoves him back down the tunnel to Drax, who removes the control box to disable the robot dog.
Proceeding down the corridors, the Doctor is captured by a mute. Meanwhile, K-9 is back to normal and requests help from Drax.
The Doctor refuses to hand over the Key of Time and the Shadow tortures Romana. The Shadow admits that he has the sixth segment and notes the Doctor has already seen it. He then says that he’ll break the time loop once he has the Key of Time, and then revel in the destruction of millions of lives. The Doctor has no choice but to agree to save Romana’s life.
With K-9’s help, Drax converts the dimensional stabilizer into a weapon and goes to help the Doctor.
As a mute accompanies the Doctor to get the Key of Time, the Shadow says that Astra’s destiny is at hand and removes the control box from her neck.
Drax sneaks up as the Doctor leads the mute to the TARDIS and starts to open the door. The repairman points the gun and opens fire… on the Doctor, who shrinks out of sight.