In the Dark Ages, the formidable Blood Queen, Nimue (Milla Jovovich), a powerful and ancient British sorceress, unleashes a devastating plague upon England. Only the knight King Arthur (Mark Stanley) and the elder witch Ganeida (Penelope Mitchell), who believes that Nimue’s reign of terror must end, can stand in her way. Together, they confront her, and Arthur wields Excalibur to dismember Nimue, burying her remains across the land to prevent her return.
Fast forward to present-day Tijuana, Mexico, where Hellboy (David Harbour), a powerful Cambion working for the Bureau for Paranormal Research and Defense (B.P.R.D.), reluctantly puts down a vampire: Esteban Ruiz, a missing agent consumed by his grim fate. With Ruiz's final words proclaiming that doom is approaching, Hellboy is summoned back to the B.P.R.D. headquarters in Colorado. There, his adoptive father, Trevor Bruttenholm (Ian McShane), tasks him with assisting the Osiris Club, an enigmatic society that investigates the occult, in their mission to hunt down three giants.
However, a seer from the club, Lady Hatton (Sophie Okonedo), warns Hellboy of a dark past—he was meant to be killed by Bruttenholm when summoned by the Nazis in Project Ragnarok back in 1945. As Hellboy grapples with this revelation, the feral fairy Gruagach (played by Stephen Graham and Douglas Tait) restores Nimue, planning a revenge scheme against Hellboy.
During his quest, Hellboy is deceived and nearly slain by the Osiris hunters, who viewed him as the “end of the world” threat. In a moment of desperation, he defeats the giants that were meant to bait him before being rescued by Alice Monaghan (Sasha Lane), a young woman with ties to magic from her own troubled past. After a tumultuous ride back to safety, Hellboy discovers that someone is attempting to reclaim Nimue's remains from the Osiris Club.
Upon their shocking arrival at the club, Alice connects with Hatton's spirit, discovering that Nimue's goal is to use Hellboy to usher in the apocalypse. With her forces gathering, and the traits of her past haunting Hellboy, he confronts Gruagach, only to find that the ogre holds years of spite against him.
In a dramatic twist, agents like Ben Daimio (Daniel Dae Kim), a soldier with a dark secret, become entwined in Hellboy's fate as plans for treachery unfold. Relationships are strained through brutal confrontations, and Hellboy’s own nature comes into question amidst the chaos that ensues.
After a whirlwind of events leads them to Merlin (Brian Gleeson), who reveals that Hellboy is a descendant of Arthur—a conflict of identity ignites. When the wisest minds fail and alliances begin to crack, the fate of London hangs in the balance as Hellboy struggles against Nimue's full resurrection.
In an emotional climax, amid epic confrontations and his own internal battle, Hellboy must choose between his inherited destiny and the relationships he’s formed. His actions release a horde of demons when Nimue seizes power, forcing Hellboy into a moment of reckoning.
As the dust settles, victories and losses weave a complex tapestry of sacrifice and legacy. Hellboy and his allies band together to confront the remnants of their past, securing what’s left of their world. However, ominous hints of resurgent threats linger in the air, as a grave secret unfolds in a post-credits scene with Baba Yaga stirring dark forces to pursue Hellboy once more, leaving the audience questioning what lies ahead.
