The Doctor realizes that Mentalis can’t attack, because it’s been programmed to stop. However, it will self destruct rather than accept defeat, once the Marshal attacks. The Doctor points out that the Shadow is manipulating all sides in his attempts to gain the sixth segment of the Key of Time.
The Shadow goes to see the imprisoned Astra and attaches a control box to her neck, placing her under his control.
The Doctor tells Shapp and Merak to go back to Atrios and convince the Marshal to stop his attack, while he attempts to disarm Mentalis. Merak is concerned about Astra but Romana tells him his first duty is to his patients. As Merak leaves, he hears Astra calling to him. He follows the voice while a mute opens fire on Shapp, stunning him and sending him back into the transmat where he’s teleported to Atrios.
Merak moves through the Zeon corridors and finally finds Astra. He reaches for her… and passes straight through her image, falling into a black void.
The Doctor continues to work on Mentalis, having K-9 make sure that Mentalis doesn’t perceive his efforts as a threat. Romana wonders where the Zeons are and concludes the Shadow has Astra. She points out that the Shadow must have a third planet and is using it to obstruct the signals between Atrios and Zeon. The Doctor goes to work and manages to open the panel. He triggers the primary alert signal, activating Mentalis’ defenses.
The Marshall approaches Zeos and prepares to launch a missile assault. On Zeos, K-9 detects the Marshal’s approach and they realize Shapp has failed. Mentalis begins its self destruct sequence and fires on its own control center to prevent the Doctor from interfering. The Doctor gets an idea and runs to the TARDIS. He puts the five segments together and uses the Tracer to lock them. He realizes they won’t operate with the sixth piece, but he can create an artificial piece to power the Key of Time.
Shapp recovers consciousness and signals the Marshal, who ignores the signal and prepares to achieve final victory.
The Doctor builds a piece out of chronodyne as K-9 warns that it will quickly deteriorate. The Doctor adds the piece and creates a neutral timeless zone around the Marshal’s ship. The Marshal opens fire… and opens fire… and opens fire. Mentalis’ countdown is locked into a three-second time loop. K-9 points out that the deterioration increases as they stop a larger area. They only have 3.25 minutes. They quickly localize the time loop by commanding the Key of Time to confine the time loop to the Marshal’s ship and the Zeon computer room. However, K-9 warns that the time loop is slowly deteriorating.
The Shadow, aware that the Doctor has used the Key of Time, orders Astra to help him gain access to the TARDIS and sends two of his mutes with her. As the Doctor and Romana return to Mentalis, Astra transmats to Zeos and calls out to Merak, who is injured. She “rescues” him and takes him to the TARDIS, where K-9 is guarding the vessel. He recognizes Merak but is suspicious of Astra. The mutes attack and K-9 drives them off. Astra approaches the TARDIS and insists she must get in, but Merak explains only the Doctor and Romana can enter it. She says that they must find the Time Lords.
The mutes escape K-9 via the transmat chamber. The door opens, revealing a glowing box giving off a signal. K-9 recognizes a galactic computer distress call and asks for identification. He gets no answer and enters the transmat link, and is teleported away.
Astra and Merak find the Doctor and Romana. The Doctor is curious to know how Astra escaped, and suggests she go back to the transmat and return to Atrios to alert her people. She leaves with the injured Merak.
K-9 arrives in the Shadow’s lair and starts exploring.
Astra releases the injured Merak and calls him a fool. She departs with two mutes who return to the planet. Merak limps to the transmat and teleports away. Astra runs to the TARDIS and finds the Doctor and Romana. They open the TARDIS and go inside, where Astra is fascinated by the partially-assembled Key of Time. The time loop has stretched to five seconds, giving them an hour of real time. The Doctor notices Astra’s interest in the Key and asks if it triggers any hidden memories. Astra claims not to remember anything.
As the Doctor and Romana pilot the TARDIS to the Shadow’s planet, the Shadow is waiting for him… with K-9 under his control.