The Minoan Empire has been experiencing a golden age, but now, for no apparent reason, the village of Akrotiri on the island of Thera is being attacked by fiery demon bulls that age whatever and whomever they touch to dust within seconds. The potter Alcestis is appalled by her fellow citizens’ response to the attacks. Rather than pulling together, they have become guarded and suspicious; some are taking personal advantage of the confusion, and many support their own prejudices by blaming the attacks on traitors or foreigners.
While walking in the fields outside the village on day, Alcestis sees a man descend from the sky. This is the Doctor, who has detected ripples in the fabric of Time around the islands. The temporal turbulence has prevented his ship from materialising, and he has left it hovering in mid-air while he descends to the islands on multi-coloured parachute wings. Unfortunately, an updraft from the volcano on Kaménai blows him off-course to Thera, where the soldiers, alert for any signs of strange behaviour, refuse to let the Doctor cross over to the royal island.
The Doctor is thus stuck in Akrotiri when another demon bull attacks, and he intervenes to keep the bull distracted and protect the people in the marketplace. Alcestis instinctively leaps in to help him, and finds that she can somehow predict which way the bull will move before it does so. The bull dissipates into smoke, and when the Doctor questions Alcestis, she admits that she used to be a priestess on Kaménai before the high priestess, Britomartis, expelled her for “poor discipline”. She always regarded the Titans with awe and wonder, and she has retained that sense of wonder, which may be why she is able to sense the temporal currents washing about the islands. The Doctor teaches her to refine her abilities, and soon, she has developed the ability to step into the temporal currents and let them support her flight through the air.
After a great deal of practice, Alcestis becomes capable of controlling her flight, and the Doctor then teaches her to tap into her inner rage and focus it, using it to control her dance through the air. To Alcestis’ surprise, even though the Doctor has taught her so much, he must admit that he is himself incapable of stepping into the currents; he can only sense them from the outside, looking in. He also reveals that he has deduced the nature of the bulls, which he saw as something quite different. They are the raw forces of Time unleashed -- and since the disturbance is centred on Kaménai, this implies that someone at the heart of the empire is responsible for the attacks that may tear it apart.
Alcestis senses a change in the currents, and realises that another attack is due. The Doctor weaves his parachute wings into a costume which will help Alcestis to confuse and distract the bull when it attacks. Using the lessons the Doctor has taught her, Alcestis lures the bull to an already-damaged area of the city, tires it out with her ducking and weaving, and then leads it up into the sky, where the bull runs out of energy and dissipates. Not a single person has been harmed in the attack, and Alcestis picks up the Doctor and flies him to the docks, where the stunned soldiers agree to take them both to the royal palace on Kaménai.
The Doctor introduces himself to King Rhadamanthys as Perdix, using the name of the innocent victim killed by the traitor Daedalus. Rhadamanthys agrees to accept him as a consultant, and also requests that he act as teacher to the princes Glaucus and Deucalion. Meanwhile, Alcestis speaks to Britomartis, eager to be accepted back into the priesthood so that she may once again feel the touch of the Titans in her mind during the blessing ceremonies. Britomartis reserves judgement, unsure whether Alcestis has truly learned humility or still believes her own dance to be more important than the collective dance of the temple.
The Doctor and Alcestis deliberately waste time when ordered to look for others who may share Alcestis’ gift, and in fact use their positions to observe the courtiers and servants, looking for the person responsible for the attacks. Things change when the Doctor deliberately makes a provocative remark about the King’s power, and Rhadamanthys shows him the source of that power -- the Titans themselves, fallen gods imprisoned within crystals in the volcano and bound to obey the commands of the King. Rhadamanthys, secure in his position of power, does not listen to the Doctor’s warning that even his empire must one day fall. It’s clear that Rhadamanthys himself cannot be responsible for the attacks; however, nobody else in court seems to be. In fact, the councillors blame the city of Athens, which recently lost a devastating war with the Minoans after the city was struck by plague. Convinced that the Athenians are out for revenge, the King’s councillors are beginning to suggest that they should unleash the Fallen upon the city of Athens before it’s too late.
In the midst of the social chaos, the King announces that Glaucus, who is about to turn 13, is to be sent away for military training. The Doctor and Alcestis bid a fond farewell to the intelligent young prince -- but that night, Rhadamanthys and Britomartis lead Glaucus to the temple of the Fallen, and Glaucus ages to dust within seconds. Alcestis senses the disturbance in the currents, and she and the Doctor confront Deucalion, who admits that this has happened before. The King farms out children on his servants, raises them to 13 years of age -- and then has the Fallen take the rest of their lives away to share between the King and Deucalion. Deucalion is appalled by the cost of his “gift”, but he is unwilling to speak out against his father, for fear that he will suffer the same fate as his brothers. Alcestis is particularly horrified by this revelation, and admits to the Doctor that, despite her youthful appearance, she is 48 years old. The priestesses of Rhea have used the blessing ceremonies to spread the gifts of the Titans throughout the empire, and their own lives have been extended as a result -- but for the first time, Alcestis realises that the “gifts” were stolen from others. Who has paid the price for the Minoan golden age, and for Alcestis’ own extended life?
The Doctor visits the Fallen’s temple once more, finally recognising them for what they are -- beings which have evolved to live outside linear Time, but which have been trapped within the crystals by multi-dimensional mathematics. Realising that the King is incapable of harnessing the Titans’ power, Alcestis departs to confront Britomartis. In her rage, Alcestis plucks the high priestess up above the island and threatens to drop her unless she confesses the evil she has done; however, Britomartis genuinely believes she was justified in her actions, which she made to protect the empire. To Alcestis’ horror, Britomartis reveals that the years of bounty which have extended the empire’s golden age were stolen from Athens. The “plague” which struck down the enemy was caused by the Fallen, and Alcestis herself participated in the “victory prayer” which stole the centuries from their enemies. Furious, and sickened by Britomartis’ refusal to accept that what she’s done is wrong, Alcestis drops down to the island and smashes Britomartis against the cliffs, killing her instantly.
Meanwhile, the Doctor attempts to communicate with the Fallen and learn who is using them to attack the empire, only to realise that the Fallen are themselves responsible. Enraged by the constraints enforced upon them by the Minoans, they intend to force Rhadamanthys to unleash them upon his perceived enemies -- at which point, the Fallen will be free to turn on their former captors and destroy them. The Doctor offers to find a way to free them peacefully, but the Fallen want their revenge, and they turn their power on the Doctor, who barely makes it out of the shrine alive. When Alcestis returns, the Doctor is too weak to realise what she’s saying until it’s too late. Numbed by Britomartis’ revelations and subsequent death, Alcestis now knows that the entire empire shared in Athens’ downfall. Realising that Alcestis intends to make everyone in the empire pay for the crimes committed in their name, the Doctor tries to warn her away from this path, but she cannot forgive such a monstrous crime -- and she leaves the Doctor, no longer trusting his show of innocence, and convinced that he too must have taken the lives of uncountable others to be as pure as he appears.
Alcestis thus returns to Akrotiri to tell her fellow citizens what she’s learned, but her tale goes unheeded. Some don’t believe her; some don’t understand her; some believe the Athenians deserved their fate; some are too crushed by the horror to react; some use her story to support their own self-centred ranting against the empire. When another demon bull attacks, Alcestis tries to stand by and let it happen, but finds herself unable to watch as others suffer and thus intervenes; however, she is distracted and nearly loses her life. Filled with rage and with nowhere to direct it, Alcestis flies back to the palace.
Back on Kaménai, the Doctor takes a fire crystal from the volcano and uses it to trap the spent temporal energy from the demon bull attack. He then builds a telescope and uses it to prove to Rhadamanthys that the Fallen themselves are releasing the demons. If they are unleashed again, they will destroy his empire. As the stunned Rhadamanthys retreats to consider this, Alcestis attacks the Doctor; she has overheard everything he said, and is enraged with him for making a deal with a man who would his children and unleash the Fallen upon Athens. She is equally enraged with the Doctor for showing her these truths and making her deal with them herself. The Doctor fights her off, and she retreats to the temple of the Fallen for comfort -- where she becomes convinced, rightly or wrongly, that the Fallen have given her these powers so that she may be the one to put things right.
Determined to make the Doctor admit his own guilt in this matter, Alcestis comes to him as he sleeps, lifts him high above the island and drops him. However, even as he falls, she realises that he is still more afraid for her than of her. Enraged, she plummets and grabs him moments before he hits the island, but he stops her from touching down, warning her that their bodies still retain the momentum of their fall. At his urging, she flies out to sea before releasing the currents, and both she and the Doctor survive their plunge into the water. Once again he’s saved her life, and once again she assumes that he’s missed the point of her “lesson”. The Doctor tells her that the empire will fall, but far in the future, when everyone responsible for the crimes against Athens is long dead. She does not accept this as justice, but she does offer the Doctor a chance to leave the empire before she unleashes the Fallen.
As Alcestis departs, she informs the Doctor that a blessing ceremony is to be held the next day, and the Doctor realises almost too late that this will give the Fallen the chance they are looking for to launch their attack. Fearing that his citizens will revolt if their expected blessings are withheld, Rhadamanthys allows the ceremony to proceed, but orders Deucalion to remain in the palace where it’s safe. As the Doctor had feared, when the ceremony begins, the Fallen slip their bonds and unleash the demon bulls upon Kaménai itself. In the chaos, the Doctor offers to save Rhadamanthys on the condition that he confess his crimes, and the King does so, publicly admitting that his actions have brought this disaster upon the empire. The King’s courtiers abandon him, but before the Doctor can stop her, Alcestis descends, carries Rhadamanthys over the volcano, and drops him in.
Alcestis then joins the priestesses conducting the blessing ceremony and sweeps into the dance, guiding it into a new pattern -- one which will unleash the Fallen upon the empire, destroying all. Unable to reason with her or to interrupt the dance, the Doctor has no choice but to stab Alcestis through the chest with a steel dagger which he forged earlier. As the dance breaks up, the bulls dissipate -- but Alcestis, enraged that the Doctor could do such a thing to her, descends into the currents, into a frozen moment of Time in which the Fallen heal her wound.
Deucalion is now King, and after accepting his new royal name, his first act is to declare an end to his people’s golden age. He cannot return the stolen years which were given to him, but he can use them to learn how to guide his people wisely. On his orders, the surviving palace guards use catapults to smash apart the temple, scattering the crystals far and wide to ensure that the Fallen will not be able to attack the empire again. The Fallen send more demon bulls to stop them, but the Doctor holds them off, riding the currents with his parachute wings and the fire crystal which he charged up earlier.
Alcestis attempts to kill Deucalion for his part in his father’s crimes, but the Doctor saves his life; however, as the Doctor and Alcestis struggle, they fall into the volcano, and the Fallen transport them to another plane of existence. The Doctor is chained to a mountain, and Alcestis is transformed into an eagle, who repeatedly tears the Doctor’s flesh apart to devour his heart. Despite his agony, the Doctor still refuses to break and give Alcestis what she wants, and as the torture goes on it becomes to seem ever more pointless and wearying even to her. Eventually, she ends up begging the Doctor to break just so they can get out of here, but he reveals that they never will. The Fallen have no further use for Alcestis, and have thus put her into this time loop to punish her for failing to release them. She wants a cathartic release from the pain she’s suffered and caused, but there will be no ending for her, because nothing ever really ends. As Alcestis collapses in tears, the Doctor grabs her by the throat, but despite all she’s done to him in this torture room, he manages to stop himself from choking her to death. He has always accepted his guilt for the things he’s done, and he’s always tried to be better than those whose deaths he’s responsible for -- because if he isn’t, then the best really did die.
Alcestis finally understands and accepts the Doctor’s position. The mountain then fades away around them; as the Doctor had hoped, the Fallen’s power had already been scattered when they fell into the volcano, and the time loop is not eternal. He and Alcestis have one brief moment to ride the currents up out of the volcano, but with the crystals scattered, the currents are dying away -- and the Doctor’s fire crystal is interfering with Alcestis’ ability to fly. Now, at last, when she no longer wants him dead, she must let him fall to save herself. The Doctor urges her to do so, and she thus splashes down safely, but alone. When she surfaces, there is no sign of the Doctor -- although she does hear a strange noise which might be the sound of his ship, finally able to negotiate the dying currents and reach him. Knowing she will never see the Doctor again, Alcestis returns to the island to face the consequences of her own actions.