Thatch is a wych, dead for two hundred or so years at the time of the novel. The Fraternity had installed her spirit into the body of Alaizabel Cray, intending that Alaizabel would die so that Thatch could live again, but Aliazabel's will is too strong. Alaizabel and Thatch battle within Alaizabel, and Alaizabel is stronger. The spirit of Thatch is eventually removed from Alaizabel and put into another young woman, but remnants of Thatch's power remain within Alaizabel. Thatch is central to the Fraternity's plan to summon the Glau Meska, but the portal from death to our world is shut when Thaniel kills Thatch.
