Warriors’ Gate was the fifth story of the 18th season of Doctor Who. It saw the departure of Romana II and K9 from the regular cast and concluded the “E-Space trilogy”.
From a production standpoint, it marked Graeme Harper’s directorial debut on the program, although he wasn’t credited in that capacity for his work. His promotion to the director’s chair followed one of the rare instances that a director was fired during production of a Doctor Who story — although credited director Paul Joyce was quickly re-hired.
A countdown takes place, leading up to the crew of a spacecraft using a Tharil to attempt to escape from “nowhere”. They fail. On board the TARDIS, the Fourth Doctor is at the controls. They have entered a disruption and the Doctor struggles to make sense of it. The Tharil, Biroc, is taken away but escapes from his escort. He is seen by Lane, who warns the bridge. Meanwhile, the Doctor is trying to land the TARDIS. He moves to press a button but Romana prevents him from doing so because it is dangerous. He considers if he subconsciously wanted to press the button.
Romana is still trying to avoid returning to Gallifrey. She asks the Doctor if they have the right to take Adric out of his own time. The Doctor tells her Adric will love it on Gallifrey. Adric decides to press a button and does so, determined by flipping a 100 Imperials coin, a method suggested by the Doctor. Biroc has escaped the craft and runs through a white void.
The TARDIS lands and the console sparks. Smoke pours out of K9. The Doctor avoids the time winds coming through the open doors of the TARDIS as Biroc enters and walks to the controls. On the spacecraft, they pick up the TARDIS on their scanners, noting it as a craft. Biroc begins operating the TARDIS controls. The Doctor and Romana note that he is on a different time line, prompting Romana to wonder why he hasn’t been torn apart. On the craft, Captain Rorvik decides to wake another Tharil up to navigate them out of the “gap between timelines”. He announces that they are to go out to the TARDIS. Biroc speaks with the TARDIS crew; he tells them not to trust Rorvik and his men. He says he (Biroc) is a “shadow of his past, and your future” to the TARDIS crew, and then he leaves to cross the white void.
The Doctor shows Romana the co-ordinates, all zero. He leaves to follow Biroc, after telling K9 to follow him but then realizing he has been damaged by the time winds; he finds a sign of life in K9 and then sets off. Romana tells Adric that they are in the gap between the negative co-ordinates of E-Space and the positive N-Space, which Adric likens to an intersection. The pair set about repairing K9, who warns them of three approaching humanoids. Using a mass detector, Rorvik and two of his crew search for the craft they picked up. The TARDIS crew see them approaching on their scanner.
Biroc arrives at a stone arch with a door in it; he enters and is closely followed by the Doctor. Inside, Biroc inspects a cobwebbed dining hall. He passes through what appears to be a mirror and disappears. Rorvik’s group are inspecting the TARDIS. They cannot determine what it is. The Doctor arrives in the dining hall and makes his way around it. He inspects two skeletons in armor, brushing off cobwebs he moves on; one skeleton moves. The Doctor crouches by the mirror as the skeleton advances on him; it raises its axe and swings.
The Doctor notices the skeleton attacking him just in time to dodge its axe. A cat and mouse game ensues with the Doctor impersonating a skeleton by keeping still and holding an axe in his hand. However when the Doctor attempts to move away, the skeleton spots him trying to escape and cleaves the axe shaft in two.
Meanwhile back on the TARDIS, Romana and Adric are arguing about the trustworthiness of the men from Rorvik’s crew outside, with Romana deciding to exit the TARDIS and introduce herself to the men, ordering Adric to stay put. They both have a conversation with Romana commenting on the mass detector and Rorvik questioning her on the whereabouts of Biroc, with Romana commenting on the subjectivity of memory. After explaining the problems concerning their ship, Romana then gives a signal on cue signalling danger before being escorted by Rorvik’s men. After they leave Adric peeks outside the TARDIS doors.
In the abandoned building, the Doctor is confronting two skeleton warriors when he points out that he “usually gets along with machines so well”. The Doctor tricks the skeletons into killing each other by staying still and letting them hit each other with their weapons, thus getting himself out of a predicament.
Adric and K9 exit the TARDIS against Romana’s orders to follow her, with K9 experiencing calculation errors due to the damage sustained earlier. Adric tells K9 to stay put and while he is away, K9 manages to restore calculation errors. In the spaceship, Romana is hooked up to navigation equipment exactly like Biroc was earlier, but is initially found ineffective in controlling the navigation equipment. As a result of this failure, Rorvik announces to his crew that they need to bring more Tharils out of hibernation to be navigator, despite his own acknowledgement of the risks involved in their survival.
However when an image on the navigation screen is found, the crew decide that Romana is useful as a navigator and leave her in the seat despite the risks. Rorvik decides to exit the spaceship with his crew when one of them can’t come out due to a leg injury. This however turns out to be a ruse as the same man along with his companion walk normally with the door closing behind them.
Back at the building, the Doctor attempts to extract information out the skeletons by tweaking their machinery with a sharp dagger. After a few taps a mechanical voice from the fallen skeleton identifies itself as the “Gundan” whose directive is to “kill the brutes”. It emerges that the Gundans are machines designed by human slaves of the Tharils to fight back against their masters, who fled to safety through the “gateway”. When the Doctor attempts to find out the exact nature of the gateway, the Gundan shuts down from power failure, frustrating the Doctor when the conversation was “just getting interesting”. The Doctor wishes that an alternative power source was nearby when he is surprised by K9’s arrival. The Doctor uses K9 to obtain more information from the machine, who reveals that there are three gateways and they are one, implying that although they are different entrances, they have the same exit and that the “masters” came from the gateway.
While this is happening Rorvik and his men find the Doctor talking to the machine and just when they were getting very close to finding out the gateway’s secret, one of the Gundans decapitates the other Gundan and then retreats through a gateway. During the chaos the Doctor escapes with K9, who is even lower on power supply, and when the crew catch up to the Doctor, he escapes through a gateway by walking backwards into it.
Back on the spaceship, two of the crew members staying behind wheel out one of the hibernating Tharil and manage to revive the creature with a large electric shock presumably at the cost of their lives. The creature emerges from underneath its covering and finds the navigation deck with Romana still trapped in the chair. She screams as the Tharil touches her with its hand.
The Tharil, whose name is Lazlo, frees Romana. When Aldo and Royce search for him, he hides, and Romana pretends she is still connected to the machine.
The Doctor can see Rorvik and his men on the other side of the mirror. Biroc explains to the Doctor that the mirror is a gateway to E-Space. The Doctor’s damaged hand is healed by the time winds, and K9 can pass through the mirror and be healed, but for him it wouldn’t be permanent. Biroc and the Doctor go to a mansion.
K9 is getting worse, and when he hears Packard and Lane discussing odd readings, K9 decides to investigate. Packard and Lane have noticed that distances seem to be getting shorter. They go back to the ship, seen by Adric, who follows them and meets up with Romana. Romana and Adric follow Lane to the damaged area of the ship and discover that the ship’s hull is made of dwarf star alloy. K9 finds Romana and Adric, repeating warnings. Adric tries to shut him up, and Romana is captured by Lane and Packard.
In the ship Lazlo rescues Romana and takes her to another timeline. Adric and K9 hide on the MZ laser which the slavers are taking back to the Gateway. In the Gateway, the men see Lazlo and Romana pass through the mirror.
Lazlo is healed, and he and Romana go to the mansion. They see the Doctor and Biroc eating at a table with Tharils. Biroc tells the Doctor the Tharils crossed the timelines to build an empire, enslaving humans. When the Tharils turn on the Doctor, Romana runs to him. Gundan robots enter, signalling the start of the human rebellion. The Doctor and Romana suddenly appear in the same hall but at a different time, surrounded by Rorvik and his men.
Rorvik won’t listen when the Doctor says only time-sensitives can go through the mirrors. K9 arrives and tells the Doctor that the dwarf star alloy in the slavers’ ship is causing the Gateway to contract. Rorvik threatens the Doctor, who is standing near the mirror. Biroc, on the other side, tells him to do nothing.
Adric arrives and threatens the slavers with their own MZ laser. The Doctor and his friends escape. The slavers see their ship just outside and realize the Gateway is contracting further. They fire at the mirrors but are unable to break through.
Rorvik decides to use a backblast to break the mirrors, but the Doctor realizes it would destroy everything. He and Romana head for the ship to short out its power. Meanwhile, Rorvik has his men revive the Tharils, aware that most may not survive, because they will need a navigator. Sagan tries to revive the Tharils, but trying to speed up the process doesn’t work, electrocuting the Tharils instead.
Rorvik finds the Doctor and Romana, but they are rescued by Biroc, who brings them to safety of the TARDIS. The Doctor now understands why Biroc told him to not do anything. Lazlo kills Sagan and revives the rest of the Tharils.
Romana informs the Doctor that she is staying in E-Space to help Biroc free his people. K9, unable to function on this side of the mirror, stays with her.
Rorvik starts up his engines, and Biroc takes Romana and K9 through the mirrors while the TARDIS de-materializes. The energy from the backblast destroys the slaver ship, but the Tharils are able to phase to a different timeline and escape the destruction.
The TARDIS returns to N-Space. Romana and K9 are ready to start their new lives.