The Lair of the White Worm recap

Adam Salton returns from Australia to live with his great-uncle in an English district dominated by ancient estates and older legends. He befriends Sir Nathaniel de Salis and falls in love with Mimi Watford, whose cousin Lilla is being subjected to the obsessive mental influence of Edgar Caswall, the new master of Castra Regis. At nearby Diana's Grove, Lady Arabella March conceals a monstrous connection to a vast white worm dwelling beneath the estate. Caswall's experiments with mesmerism and an enormous kite grow increasingly destructive; Lilla dies under the pressure of his attack, while Arabella kills Caswall's servant Oolanga when he threatens her secret. Adam and Sir Nathaniel trace the supernatural danger to the Grove. Adam mines the site with explosives, and during the final storm Diana's Grove and Caswall's tower are destroyed. The white worm, Arabella, and Caswall perish, leaving Adam and Mimi alive to begin their life together.

Adam Salton arrives from Australia after accepting an invitation from his elderly great-uncle Richard, owner of Lesser Hill. Richard hopes Adam will settle in the ancestral district and eventually inherit his property. Adam is welcomed warmly and meets Richard's friend Sir Nathaniel de Salis, whose knowledge of local history includes traditions reaching back to Roman and prehistoric Britain. The neighboring estate of Castra Regis is also changing hands: Edgar Caswall has returned from Africa as its new master. Another prominent neighbor is Lady Arabella March of Diana's Grove, an imposing woman whose elegance masks serious financial pressure. Adam is immediately intrigued by both the old landscape and the strong personalities gathering around it, while Sir Nathaniel's stories suggest that the countryside may preserve dangers as well as memories.

Adam meets Lilla and Mimi Watford at Mercy Farm and is drawn to Mimi, while Edgar Caswall becomes intent on mastering the gentler Lilla through concentrated force of will. Mimi resists on her cousin's behalf, turning the contest into a struggle between Caswall's dominating stare and the women's mutual loyalty. Caswall's servant Oolanga watches the district with a mixture of fear and calculation, paying particular attention to Lady Arabella. Strange deaths and the behavior of animals around Diana's Grove deepen Adam's unease. Drawing on his experience with dangerous wildlife, Adam acquires a mongoose, while Sir Nathaniel begins connecting the present disturbances with the legend of a gigantic primitive creature said to have survived beneath the land.

Caswall continues his effort to overpower Lilla and explores instruments associated with an ancestor's occult experiments. He also raises an enormous kite over Castra Regis, and its prolonged presence becomes another oppressive influence on the neighborhood. Adam and Sir Nathaniel investigate the ground around Diana's Grove, where unnatural sights, foul traces, and sudden violence support the possibility that something vast moves through hidden passages below. Lady Arabella cultivates Caswall while also approaching Adam, but Adam remains devoted to Mimi. The conflicts now overlap: Caswall wants control over Lilla, Arabella seeks wealth and security, and Adam and Sir Nathaniel are trying to protect the Watford household while learning what inhabits the Grove.

Oolanga's spying brings him too close to Lady Arabella's secret. His attempt to confront and exploit her ends with his death in the hidden pit at Diana's Grove. Adam and Sir Nathaniel are increasingly convinced that Arabella is inseparable from the ancient white worm, a creature capable of taking or using human form and retreating through the well beneath her house. At Castra Regis, Caswall's fixation on Lilla intensifies rather than weakening. Mimi tries to shield her cousin, but Lilla cannot withstand the sustained mental assault and dies. The loss confirms the human cost of Caswall's obsession and leaves Adam and Mimi more determined to oppose the threats surrounding both estates.

With Lilla dead and Oolanga gone, Adam and Sir Nathaniel focus on destroying the creature beneath Diana's Grove. Adam's direct encounters with the white worm confirm that ordinary precautions will not be enough. Lady Arabella's plans involving Caswall collapse as suspicion and hostility replace their temporary alignment, while Caswall becomes more isolated within his tower and absorbed by the great kite and his experiments in influence. Adam secures control of the threatened property and prepares explosives around the worm's underground refuge. He and Mimi bind their future together, but their survival depends on completing the attack before the creature can escape or strike at them again.

Adam finishes laying explosives around the well and caverns of Diana's Grove. A violent electrical storm gathers as Lady Arabella returns to the lair and the great white worm emerges in its final attempt to survive. The charges explode amid the lightning, demolishing the Grove and destroying Arabella and the creature. The storm also brings down Caswall's tower, killing him and ending the oppressive influence centered on Castra Regis. The ancient survival Sir Nathaniel feared is wiped out along with the two estates that sheltered the book's threats. Although Lilla and Oolanga have died, Adam, Mimi, Richard, and Sir Nathaniel live through the destruction. Adam and Mimi remain together, able to face a future no longer governed by Caswall's obsession or the predator under Diana's Grove.

After identifying the creature beneath Diana's Grove, Adam prepares to destroy its refuge with explosives while Sir Nathaniel helps him interpret the danger. Lady Arabella, now openly revealed as the human form associated with the ancient white worm, returns to the pit during a violent storm. Adam's charges detonate as lightning strikes across the district, tearing apart Diana's Grove and killing the monster. Caswall's tower at Castra Regis is also destroyed, bringing his destructive campaign of mental domination to an end. Lilla and Oolanga have already died in the struggle, but Adam, Mimi, Richard Salton, and Sir Nathaniel survive. Adam and Mimi are left together, freed from both Caswall's persecution and the predatory force that had haunted the neighborhood.