Thorne Malkin is a character in the Spook's: I Am Grimalkin and Spooks: Alice.
The section below contains spoilers, do not read if you haven't read the books!
Thorne and Grimalkin met one day when Grimalkin was meditating by the trunk of a tree, and Thorne came up to her and kicked her. At the time, Thorne was a little girl, 10 years old. Grimalkin then procedes to lift Thorne by her hair, telling her that if she kicks her again, she will cut off her foot. Thorne then tells Grimalkin that both of her parents died, and that she is being raised by her uncle, who beats her everyday. Thorne then asks Grimalkin to kill her uncle. Thorne then asks Grimalkin to train her as a witch assassin, so Thorne can replace her when she dies. Grimalkin, however, turns Thorne down. The next day, Thorne approaches Grimalkin while she is sharpening a blade, and attempts to kick her again. This time, Grimalkin is ready. She blocks the girl, and throws her to the ground. Grimalkin then allows Thorne to come with her to kill a bear. While Grimalkin expected the girl to run from the bear she was brave and attacked it, which almost provoked the bear into killing her. But Grimalkin saved Thorne few seconds from death and killed the bear just in time. Grimalkin then agreed to train Thorne.
Years later, Grimalkin has been poisoned by the claws of the kretch, and calls upon Thorne to help her get to Agnes Sowerbutts, a healer and Alice Deane's aunt. Although healed, Grimalkin will still have long term affects due to the poison. Grimalkin described this as a shadow of herself. Thorne then follows Grimalkin as they attempt to keep the head of the Fiend away from the kretch. At one stop, Thorne starts having feelings for the son of a knight, Sir Gilbert. The son's name is Will. However, Will betrays Thorne and Grimalkin, and they are forced to flee his company. Eventually, Grimalkin and Thorne find their way into Witch Dell to confront the kretch. However, witches light the Dell on fire, and Grimalkin and Thorne are forced to flee from the dell. As the kretch draws closer, Grimalkin falls ill to the effect of the poison. She tells Thorne to run, but Thorne is brave, and she stays with Grimalkin. However, the kretch appears and Thorne attacks it. As the fight draws on, Grimalkin goes unconcious. Upon awaking in the same spot, Grimalkin tries to find Thorne, and she does. Thorne's dead body is found, her thumb bones taken from her. Grimalkin sits on the ground, and weeps for the loss of her apprentice.
When Alice goes to the dark to get the Dolorous blade, she meets Thorne who is now living in the Dark and feasts on blood and flesh. She and Alice go to a lot of different domains of different gods and daimons in the Dark. When Alice and Thorne were being captured by the dead witches Bony Lizzie and Mother Malkin and the abhuman Tusk and the daimon Beelzebub, Thorne killed Tusk and cut off Beelzebub's thumbs which makes Thorne get her thumbs back. She also kill Raknid with the Dolorous blade after Alice gives it to her.