President Romana is quite upset by this fiasco, even though Co-ordinator Narvin claims that there is no such thing as a timonic fusion device. Cardinal Braxiatel reminds Narvin that he himself oversaw construction of a prototype, but Narvin in turn reminds him that it was dismantled when the Time Lords decided that its sphere of effect could not be contained safely. Braxiatel and Narvin are now the only two Time Lords who know that such a device ever existed, or so they think. Romana then receives a call from the High Monan, expressing his displeasure over the incident and suggesting that Romana begin her investigation in the Gallifreyan protectorate known as Gryben, the home of a subversive organisation known as Free Time. Before signing off, the High Monan warns that he may choose to send in his own troops should Romana fail to respond to this threat.

Meanwhile, Leela is preparing to leave civilisation behind and join the Outsiders in the wilds of Outer Gallifrey, for her husband, Andred, has vanished, and nobody seems to know what’s happened to him. Before she can cross the line between the city and the wilderness, however, K9 Mark I and Cardinal Braxiatel locate her and summon her to an urgent meeting with Romana. The Outsiders’ representative departs, telling Leela that her presence would only attract unwanted attention to their tribe, and Leela reluctantly returns to the city.

There, Romana explains that the fragile alliance between the temporal powers is under threat due to an initiative spearheaded by Romana herself. Unauthorised time travel used to be dealt with quite harshly, but Romana has come up with a more civilised answer to the problem by creating a temporal bubble world named Gryben which draws all unauthorised timeships towards itself. New arrivals’ needs are considered on a case by case basis; those whose petitions for travel are rejected, yet who claim they cannot return home, are forced to remain on Gryben. Some of the refugees have formed a resistance movement against the temporal powers, called Free Time -- and now it seems they’re becoming more than a nuisance. Since Free Time’s ringleader, Nepenthe, is human, Romana believes that Leela stands the best chance of infiltrating the group and learning what they’re up to. Leela agrees to carry out this mission on condition that Romana do everything in her power to find out what has happened to the missing Andred.

Torvald, Leela and K9 Mark I set off for Gryben, posing as a vicious mechanical criminal from the Fifth Galaxy and his two human slaves. Before they leave, Narvin slips Torvald a translocation crystal; if someone really has built a timonic fusion device, Narvin wants the CIA to have it. Leela, Torvald and K9-I materialise in a marketplace on Gryben, where Leela enthusiastically accepts an offer of cooked meat from an alien street vendor before she realises that Torvald has brought no money with him. As Leela and Torvald fight off the vendor and his angry associates, K9-I heads off to a nearby bar, looking for people with knowledge of Free Time. There, he meets the charming rogue Mephistopheles Arkadian, who offers to sell information to K9-I for the right price. When Leela and Torvald arrive, Arkadian recognises Torvald’s name -- and in exchange for an audience with Romana, he offers to give Torvald the passwords and location of the Free Time enclave. If Torvald turns down the offer, Arkadian will expose him as a Time Lord agent.

On Gallifrey, Romana and Braxiatel are pondering the threat posed by the timonic fusion device. Order is maintained in the Time Vortex by the temporal powers’ promise to protect the lesser races from threat in exchange for their agreeing to a moratorium on time-travel experiments -- but since the coalition has no defence against a weapon as devastating as a timonic fusion device, its mere existence would undermine their authority. Co-ordinator Narvin then arrives with Arkadian, who greets Romana as “Imperiatrix” before explaining his situation. Apparently, he was approached by a third party, who may or may not have represented the Monan Host, with an offer to sell black light rods on the open market, perhaps in an attempt to flush out the terrorists who were planning to construct a timonic fusion device. Arkadian turned down the offer, and soon afterwards, found himself on the run from the Monans in a stolen Monan time vessel. This is how he ended up on Gryben, facing extradition to the Monan Host world. Romana, Braxiatel and Narvin privately discuss Arkadian’s story; if true, it suggests that the Monans have engineered this threat so they can send troops into Gryben, gaining a political advantage from being seen to save a Gallifreyan protectorate from terrorists armed with a weapon of Gallifreyan design.

Leela, K9-I and Torvald follow Arkadian’s directions to the Free Time enclave, where K9-I gets them past the guard by correctly completing the Shakespearian quote “The time is out of joint”. Unfortunately, Nepenthe recognises Torvald the moment he enters, and her guards overpower the intruders, “muzzling” K9-I with a zybanium band. Leela claims not to have known that Torvald was a Time Lord spy, and Nepenthe, who believes that the Time Lords’ oppressive policies are putting a stranglehold on the efforts of human temporal pioneers, orders Leela to prove her own hatred of the Time Lords by killing Torvald. Instead, Leela turns on Nepenthe’s trusted lieutenant, having noted that he’s wearing a holographic disguise, and cuts free his false mask to reveal that he is in fact Ba’aruk. Before anyone can stop him, Ba’aruk transmits a message to his people warning that his mission has been compromised, and Monan time vessels begin to materialise on Gryben.

The High Monan contacts Romana to inform her that, as the CIA’s team has been compromised, the Monan Host is sending in its own forces to “extend support” to their Gallifreyan allies. Legally, Romana is at a disadvantage; since it is suspected that the terrorists on Gryben present a clear and present danger, the Monan Host is entirely within its rights to send in security forces to search for the suspected weapons of mass temporal destruction. Romana forcefully requests that the High Monan withdraw his troops, but to no avail -- and on Gryben, violence erupts in the streets as the Monan security forces impose “order” on the refugees.

Nepenthe orders her guards to restrain Torvald, Ba’aruk and K9-I for use as hostages, and prepares to activate the timonic fusion device. Ba’aruk offers to purchase the device from her in order to fund Free Time’s operations. Torvald scoffs, but Ba’aruk orders Leela to search Torvald, and she finds the translocation crystal, proof that the Time Lords also intended to take the device for themselves. In her surprise, Leela lets slip that she’s on first-name terms with President Romana, and Nepenthe, disgusted with her, activates the timonic fusion device. In 45 microspans, Free Time will show just how determined they are to make their point. Leela is tied up alongside Torvald and Ba’aruk, but unlike them, she feels some sympathy for their captors, knowing that it is the harsh life on Gryben which has driven them to such extremes. In any case, she believes that Romana will come to their rescue -- but Torvald believes that Romana will destroy the entire planet if she must to prevent the timonic fusion device from exploding.

On Gallifrey, K9 Mark II detects an energy release from Gryben, analyses it, and determines that the timonic fusion device will detonate within 42.6 microspans. Narvin despatches a fleet of battle-TARDISes, but when Romana attempts to lift the transduction barriers to give the refugees a chance to escape, Braxiatel countermands her order, pointing out that this would cause a stampede and the risk of thousands of casualties. The High Monan then contacts Romana and threatens to declare war if Gallifrey’s battle-TARDISes open fire on his “peacekeeping” troops.

It seems that Romana has no choice but to give the order to destroy Gryben, even though this will mean war with the Monan Host -- but if the timonic fusion device is destroyed along with Gryben, she will be unable to prove that her actions were justified. She thus gives Arkadian a weapon and orders him to take her to Gryben as his hostage, in exchange for amnesty for his crimes; that way, if the Time Lords are forced to destroy the planet, they will kill their own President, proving that they did not make the decision lightly. As Romana and Arkadian depart, Narvin gleefully anticipates a forthcoming Presidential election. While Braxiatel waits, he speaks with K9-II, wanting to understand more about the dog’s personality; he has been given to understand that one day he will own a K9 of his own, a gift from an old friend he has yet to meet. Narvin then arrives with the Inquisitor, who informs Braxiatel that Narvin has called a judicial inquiry to determine whether Romana’s actions today were justifiable. Narvin, Braxiatel and Romana have two weeks to prepare their respective cases.

Romana’s TARDIS materialises in the Free Time enclave, and Arkadian strikes a deal with Nepenthe, offering to hand over Romana in exchange for the timonic fusion device. Nepenthe thinks she’s won, but Romana informs her that quite the opposite is true. Romana was always willing to listen to the fugitives of Gryben with an open mind, and by threatening to detonate the timonic fusion device, all Nepenthe has done is prove that she and her followers can’t be trusted with the heavy responsibility of time-travel technology. Arkadian then pulls a gun on Romana, claiming that he’s decided to steal the timonic fusion device himself, but after a moment, he admits that he just did so to see the look on her face, and turns the gun on Nepenthe. Nepenthe has little choice but to release her hostages -- but as she does so, the Monan security forces burst in. There is an exchange of gunfire, Torvald and Ba’aruk are stunned, and K9-I stuns the attacking Monans -- but in the confusion, the timonic fusion device is hit.

The device’s anti-tamper switch has activated, and the countdown has accelerated; the device will explode in one microspan, and there is no way to stop it. All seems lost until K9’s over-literal interpretation of the word “device” catches Romana’s attention, for “device” is another term for a contrivance, or confidence trick. Romana stands back and allows the countdown to reach zero -- and the device shuts down and disappears into thin air. Nepenthe has been used as a pawn; whoever helped her to escape from Gryben and steal this device from the moon of Kikrit never intended to let her set it off. Instead, they were trying to manipulate Romana into destroying Gryben, which she had created in the first place, and in such a way that she would be declaring war against the Monan Host. Romana demands that Nepenthe tell her the name of her allies, but Nepenthe refuses to help the President of the Time Lords, and before anyone can stop her, she achieves her martyrdom by shooting herself.