Plot

Hellboy and a rookie B.P.R.D. agent in the 1950s are sent to the Appalachians, where they discover a remote community dominated by witches and led by the sinister local demon, the Crooked Man.

Introduce parapsychologist Bobbie Jo Song, who is tasked with delivering a spider to the BPRD but must seek Hellboy's help when things go awry. Together, they travel to Appalachia to take on the Crooked Man, who has been sent back to Earth to collect souls for the devil.

In the 1950s, B.P.R.D. agents Hellboy and Bobbie Jo Song are tasked with transporting a toxic supernatural spider to their headquarters via train. However, when they cross the Appalachian Mountains, the spider suddenly enlarges to monstrous proportions, causing their train car to overturn and allowing the spider to escape. Hellboy suspects that the spider grew due to an evil presence haunting the area, admitting that he could hear it calling to him. Left stranded, Hellboy and Bobbie Jo wander until they meet Tom Ferrell, a local who has recently returned to atone for his past sins. The agents accompany Tom to speak with Cora Fisher, a witch and Tom's ex-girlfriend, only to discover that her house is empty and Cora's body is missing.

As they wait for the demonic familiar to return with Cora's complete body, Tom recounts a time when he met Effie Kolb, a witch who drew him towards witchcraft and persuaded him to make a deal with an entity known as "The Crooked Man." Following Effie's suggestion, Tom used a cat carcass to summon the Crooked Man, believing that whatever bone he held when the entity arrived would become his lucky bone. However, the sight of the Crooked Man terrified Tom so much that he had a change of heart and discarded the lucky bone, but it would always return to him and kept him safe from harm. Tom is determined to confront the Crooked Man once and for all.

When the familiar returns with Cora's body, she reveals to Tom that the local witches want her soul. To Tom's shock, Effie arrives on a white horse to collect Cora's soul. After Hellboy threatens Effie, Tom removes the horse's bridle, which suddenly transforms into Tom's father as Effie escapes. Tom and his father share a brief moment of reconciliation before he dies.

The next morning, Tom, Cora, and the agents walk to a nearby church owned by Reverend Watts to bury Tom's father. However, Cora is attacked and killed by a demonic snake. Hellboy kills the snake, but its bites show him visions of his mother Sara, a witch who made a deal with a demon.

The survivors reach the church, where they are confronted by the Crooked Man and his servants. Tom is tempted to return to his lucky bone, but Hellboy stops him. As Hellboy battles the demonic horde, the Crooked Man attempts to entice the blind Reverend with youth and sight in exchange for Tom. However, Reverend Watts refuses to give in to temptation and blesses a shovel with Tom's lucky bone, which allows Hellboy to weaken the Crooked Man and neutralize his forces.

Hellboy and Tom chase the Crooked Man to an abandoned mansion but are attacked with traumatic visions. Bobbie Jo, believing that the Crooked Man draws power from the town's mines, finds a tunnel system through an access point under the church. She disrupts the Crooked Man's power source with a spell, which frees Hellboy and Tom from the visions, allowing them to destroy the Crooked Man.

In the aftermath, Effie ages rapidly, and Tom places the bridle that had transformed his father into a horse on her. Hellboy and Bobbie Jo are rescued, Tom feels a weight lifted from his soul, and a white horse wanders by, bearing a warning written on its hide: "Beware! I am a Witch!"