In 1650 Ireland, the quiet town of Kilkenny finds itself embroiled in conflict as the villagers struggle to comply with the demands of the autocratic Lord Protector Oliver Cromwell. His orders to clear nearby woods for farming pit them against a pack of wolves that inhabit the forest. Summoned from England, Bill Goodfellowe [Sean Bean] and his spirited daughter Robyn Goodfellowe [Honor Kneafsey] are tasked with eliminating the wolves, allowing the woodcutters to proceed without hindrance. Feeling trapped in the confines of Kilkenny, Robyn, longing for adventure, decides to sneak out with her loyal pet falcon, Merlin.
During her escapade, Robyn inadvertently injures Merlin with her crossbow while trying to fend off a wolf threatening a shepherd and his flock. To her astonishment, she witnesses a mysterious girl, Mebh Óg MacTíre, retrieve her falcon and vanish into the woods alongside the retreating wolves. Upon her return, she faces the ire of the Lord Protector, who rebukes her for her disobedience and grants Bill a mere two days to carry out the wolf extermination.
Shunned and escorted back by guards, Robyn cunningly escapes once more into the woods, where she discovers Merlin has surprisingly healed. It is here that she meets Mebh, who reveals herself to be a "wolfwalker," possessing the magical ability to heal. Mebh tends to Robyn's wound, ensuring it isn't too late. Their shared yearning for freedom sparks a bond, as Robyn learns that Mebh's mother, Moll MacTíre [Maria Doyle Kennedy], has yet to return from her quest for a new home for the pack. In a twist of fate and further defiance, Robyn attempts to convince Bill of the existence of these mystical beings and her plans for a peaceful resolution.
As morning dawns, Robyn’s first day in the scullery is interrupted by a strange calling that leads her to a hidden cage in the Lord Protector's chambers. That night, she undergoes a transformational experience, emerging as a wolfwalker herself and retreating back into the woods where Mebh greets her new identity with joy. Mebh guides Robyn through her newfound abilities, amplifying her senses and agility.
Back in Kilkenny, Robyn strives to revert to her human form and discovers the presence of Moll, another wolfwalker. Stealthily, she navigates the dangers of the Lord Protector’s manor to find Moll, who urges Robyn to persuade Mebh and the pack to leave the increasingly perilous woods. Eventually, just as she finds Moll, the Lord Protector's forces descend upon the town, prompting confrontations that escalate into chaos.
Robyn and Mebh band together against the oppressive might of Cromwell, witnessing the capture of Moll. In a desperate stand against the growing threats while balancing their duties and familial ties, both Robyn and Mebh confront the harsh realities of their choices. The situation culminates in fiery confrontations, with Robyn heroically defending Moll and ultimately leading her pack into battle against the Lord Protector’s men.
Enveloped in danger as the stakes rise, Bill ultimately finds himself forced to choose between the safety of Robyn and the demands of Cromwell. A heart-wrenching scene unfolds as Bill, under the influence of Moll's bite, transforms into a wolfwalker, turning his strength against the tyranny of the Lord Protector. During a climactic showdown, the very essence of nature rises against man, culminating in the Lord Protector's dramatic downfall.
In the aftermath, Robyn, Bill, and Mebh manage to revive Moll, solidifying their bond amidst the remnants of destruction. With futures uncertain but hope alive, they ride into the horizon with their pack, embracing their identities as wolfwalkers and harboring dreams of a new life. This journey not only unites them but also transforms them, echoing the timeless dance between humanity and nature.
