Claire Deverill was the sister of Mrs. Deverill and one of the antagonists in Raven's Gate.
Claire was a dark witch like her sister and sought to free the Old Ones but she was left to orchestrate business matters in the community. Claire was the principal of the primary school, which Jayne threatened to send Matt to because of how she saw his "delinquent" nature.
Claire Deverill resembled Jayne physically but she had a horrible orange birthmark on her cheek, and it disfigured her face. It had the bad effect of being darkly appealing as well, so one was forced to look at it.
Jayne's sister Claire made two very brief appearances in the novel, but she was a leader of a dark magic cult that wanted to kill Matt. Claire first appeared at chapter three, when Matthew was ill and had critical pneumonia, and he woke up, wondering if it was a dream or hallucination, and saw two women standing there. One had a bad mark on her cheek. Matthew was repulsed when they gave him snake's blood to drink in dark rituals. But somehow he ended up feeling better.
Claire made her second appearance in the village itself, when Jayne sent Matt to get a poison from the chemist's. Matt got into town but found the village square hostile and unnerving; every single villager came out and smiled evilly at Matthew, as if they knew something bad, he didn't. Matthew backed away, but then Claire came up. She greeted him pleasantly enough, and said she had met him before. Now Matt knew the ritual was not a dream. He remembered Claire, who introduced herself and said he may be at their school soon.
After Detective Superintendent Mallory accused Jayne of abusing Matt and threatened to have her in jail, Claire teamed up with her sister to use a dark magic spell to cause the policeman's car to speed right up off the bridge and smash into a truck and kill the detective.
The next week, Claire was around at her sister's for dinner and cooking something that looked suspiciously like human meat. Claire said to Matt how her sister told him he'd been missing school, which was an outright lie because Jayne had deliberately prevented him from going. So Claire said that modern children are horrible and should be taught a lesson.
Claire was eager for Matt to drink the drugged tea that Jayne offered him and Matt knew it was drugged so he upended the tea in secret. Claire then joined her sister whispering on the foot of the stairs and asked if Matt was asleep. Jayne said of course he was and he'd wake up with a chainsaw of a headache, and asked if Claire was ready, to which she agreed, and they drove off to the power station.
When Matt is betrayed by Sir Michael Marsh he is bought to the station to be executed. Claire does make her final appearance at the Omega One power plant which is breaking up because Matt is escaping from his murder. Claire gets out when she can and runs, screaming in rage. However, the air is too full of acid and burns her to death.