События сериала происходят в начале новой эры, когда Британия была населена очень воинственными кельтскими племенами, которые были не готовы перейти под управление иноземцев, пришедших с далекого юга. Во время римского завоевания Британии две враждующие кельтские воительницы - Керра и Антедия - вынуждены объединить силы, чтобы дать отпор римским легионам под предводительством Авла Плавтия.
Список, описание и даты выхода серий
On the eve of Solstice, Cait, a young woman belonging to Britannia's Cantii tribe, awaits a rite of passage that separates girls from women. However, 400 ships, carrying 20,000 Roman soldiers, land on the shores close by, under the command of General Aulus Plautius, to take Britannia in the name of Emperor Claudius. Cait's initiation into womanhood is interrupted by a Roman attack on her village, leaving her "betwixt" – neither girl nor woman – and everything she loves left in ashes. She is only left alive thanks to the actions of an outcast Druid, Divis, who has had unsettling visions of what is yet to come. Meanwhile, 40 miles inland, the border between the Cantii and Regni tribes is the site of constant bloodshed. A marriage, brokered by Cantii prince Phelan, takes place as an attempt at peace between the warring factions. But peace is a rare thing in Britannia, and this is no exception.
After the bloodshed comes the calm. Aware that the lack of organised resistance indicates an island already preoccupied by internal strife, Aulus intends to form an alliance to make Rome's victory in Britannia that much easier. He sends ambassadors to the Cantii and Regni to parlay. King Pellenor, King of the Cantii, vehemently rebuffs the Roman's attempt at diplomacy. His message received, Rome sends a brutal message back. Kerra, daughter of Pellenor and fearless warrior, defies her father to speak with Aulus herself in an attempt to end further bloodshed. However, her actions do not go unnoticed. Phelan's wife and Cantii queen-in-waiting, Amena, seeing Kerra as an obstacle to her ascent to the throne, uses this knowledge to sow seeds of distrust between Pellenor and his daughter. Roman negotiations with the Regni's queen, the fierce Antedia, appear more fruitful. Although Antedia has some demands of her own. Meanwhile, Aulus learns more of the Druids – those who deal in magic and speak for the gods themselves. Undeterred by the fear of the myths of the island that has begun to infect his army's ranks, he seeks out the Druids' leader – the mysterious Veran.
Having journeyed to the very underworld itself, Aulus returns to the Roman camp – his purpose renewed. But while he may think his insight into the Druids' world will seal his victory, the Druids view him with strange amusement. At the Cantii citadel, Phelan's attendance is requested by Ania – the Regni princess who was captured as a hostage during the illfated wedding ceremony. She announces to him that she is in fact an incarnation of the goddess of war, and has her own prophecy to fulfil. While sceptical, Phelan is very accommodating to his role in this prophecy. Cait, meanwhile, having parted ways with Divid under acrimonious circumstances and only just surviving an encounter with a pack of wolves, is finally able to track down her father, Sawyer. Now a prisoner of the Roman army, she arrives in time to see him brutally mutilated by Aulus' righthand man, Lucius, for attacking a Roman centurion. She plans a rescue, but she can't do it alone.
With knowledge of Kerra's secret parley with the Romans, and Amena's machinations coming to fruition, Pellenor, believing Kerra has betrayed her clan, disowns and imprisons her. The king staunchly believes the Druids are the mouthpieces of the gods, so he throws Kerra to their judgement. Both know that when the Druids cast judgement on Kerra's mother, they demanded she be flayed alive as a sacrifice to the gods, and Kerra will likely meet the same fate. Sensing the end, Kerra releases her brother Phelan from his oath to protect her. She also receives a visit from Lindon. A relative newcomer to the tribe, he is a Gallic warrior and another of Amena's husbands, married to her by order of the Druids. Along with Phelan he is one of the only people in the entire Cantii clan sympathetic to her plight, and it becomes clear their relationship is more than mere friendship. The day of judgement arrives, and Kerra is brought before Veran to meet her fate. Elsewhere, Divis lays eyes on Aulus, and sees something within him. Something more than man.
The gods have spoken. As the dust settles from the earth-shattering sacrifice, Veran names Kerra Queen of the Cantii. But she must first decide whether she will accept the gods' judgement. While Lindon offers Kerra the chance of escape, Amena, bitter and humiliated at being overlooked for the throne, drunkenly rebukes Phelan for failing to be named king. Deciding neither husband is strong enough to get her what she wants, she seeks out the Druids, intending to show there is nothing she will not do to get her crown. Phelan, on the other hand, chooses to flee the citadel with Ania, leaving his allegiance in question. Elsewhere, Queen Antedia learns of the developments at the citadel, and sends for Aulus. Antedia bears a deep-seated hatred of Kerra, originating from an ill-advised attempted marriage between her and the queen's only son that ended abruptly with his castration. With this humiliation still burning inside of her, she seals the Regni's alliance with Rome. But in return for their co-operation, Antedia asks for something unusual: the head of Veran.
Having travelled to the underworld for guidance in his quest, Divis realises it is none other than Cait who poses a threat to Aulus and must be the one to defeat Lokka. But Divis does not leave the underworld intact. At the citadel, Kerra is crowned Queen of the Cantii. Amena outwardly pledges her loyalty to the new queen, but behind closed doors conducts a dark ritual to summon a demon that will bring her to the throne. After their long ordeal, Cait and her father finally arrive at the safety of the citadel, where she and Kerra become acquainted with one another. Elsewhere, Aulus meets with Veran, where it is revealed that Aulus may have had more to do with Kerra's coronation than one might think. However, Aulus is soon put right by Veran that the gods do not bargain. At Crugdunon, Kerra makes a deal with Aulus to protect her people but then a demon arrives. For reasons she does not understand, Cait finds herself pursued on two fronts. Recognising her from the Druids' visions, Aulus orders her capture, while Divis, fully possessed by the demon Pwykka, also hunts her down. Kerra assists Cait in fleeing the citadel with her father, but such an action will cost Kerra dear.
Cait and Sawyer seek shelter in the burned remains of their old village. As she wonders if they will ever find safety again, Sawyer is able to see his daughter with new eyes. She is not the meek girl he once knew, she has changed, and so must the dynamic between them. Meanwhile, two other parties find temporary sanctuary at the ruins. Two Roman deserters, Bruno and Philo, are also hiding out there. However, Philo is catatonic after a previous encounter with Divis, and Brutus becomes too preoccupied with the village witch doctor's stash for them to present any danger. The bickering Phelan and Ania also arrive, seeking their own place in the prophecy, as well as somewhere for Phelan to take care of some toilet trouble. The peace cannot last, as during the night, Cait is visited by someone she never expected to see again and she learns of the part she must play in the prophecy.
Divis, now freed from Pwykka, rejoins Cait in an unlikely partnership and Sawyer, now understanding the journey Cait must make, believes he will only slow her down, so goes his own way after a tearful farewell. Four moons pass, and despite his best efforts to bestow his knowledge and skills on Cait, their partnership is floundering, and her guilt over leaving her blind father on his own has driven her to despair. As she falls into an inescapable depression, Aulus recruits bounty hunters from overseas to find Cait, with one particular hunter, Hella, proving to be exceptionally dangerous. Elsewhere, the siege of the Cantii citadel is in full swing. Reaching a stalemate, the war between the Regni and the Cantii has become a battle of wills between sworn enemies Kerra and Antedia, with neither queen willing to budge. With the war looking to stretch into the cold, long winter, Antedia plays her trump card: they have a man on the inside. Someone very close to Kerra.
The end is near. Cait, defiant to the last, has been captured by Hella. But despite Aulus offering a sizable bounty and a pardon for her previous crimes against the Empire, she chooses not to turn Cait in to the Roman camp as agreed. Divis, left near death from his encounter with Raven, receives a last-gasp reprieve from the land, and sets off in search of Cait. Elsewhere, Phelan and Ania find themselves in uncomfortable lodgings at the Druids' camp as they seek an audience with Phelan. Certain their part in the prophecy is important, Veran seems content to keep them waiting. At the citadel, with their food gone, the situation seems hopeless for Kerra and the Cantii – a fate further cemented by the arrival of a second Roman legion. As Rome truly shows the island of Britannia how it conducts its business, there is one more sacrifice that must be made.