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 Book 9: Grimalkin the Witch Assassin/Book 9: I Am Grimalkin or Book 12: I Am Alice!
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 proceeded to lift Thorne by her hair, telling her that if she kicked her again, she would cut off her foot. Thorne then told Grimalkin that both of her parents died, and that she was being raised by her uncle, who beat her everyday. Thorne then asked Grimalkin to kill her uncle. Grimalkin refused, asking Thorne what would happen if she did. Thorne said that she would become a witch assassin like Grimalkin. Grimalkin turned her down. The next day, Thorne approached Grimalkin while she was sharpening a blade, and attempted to kick her again. This time, Grimalkin was ready. She blocked Thorne's kick, and threw her to the ground. Grimalkin then picked Thorne up, slung her over her shoulder, and took her to a forest to kill a bear. The witch assassin handed Thorne the blade that she had been sharpening earlier and told her to kill the bear. Grimalkin noted that this was the first time she saw Thorne show fear. While Grimalkin expected the girl to run from the bear she was brave and attacked it, which provoked the bear into attempting to kill her. But Grimalkin saved Thorne few seconds from death and killed the bear just in time by shooting a knife into it's eye. Grimalkin then agreed to train Thorne.
Years later, Grimalkin has been poisoned by the claws of the kretch, and called 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 followed Grimalkin as the two attempted to keep the head of the Fiend away from the kretch and the servants of the Fiend. At one stop, Thorne started having feelings for the son of a knight, Sir Gilbert. The son's name was Will. However, Will betrayed Thorne and Grimalkin after Sir GIlbert was slain by the Kretch, The 2 were forced to flee his company. Eventually, Grimalkin and Thorne found their way into Witch Dell to confront the kretch. However, witches lit the Dell on fire, and Grimalkin and Thorne were forced to flee from the dell. As the kretch drew closer, Grimalkin fell ill to the effect of the poison. She told Thorne to run, but Thorne was brave, and she stayed with Grimalkin. However, the kretch appeared and Thorne attacked it foolishly. As the fight drew on, Grimalkin fell unconcious. Upon awaking in the same spot, Grimalkin tried to find Thorne, and she did. 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 went to the Dark to get the Dolorous Blade, she met Thorne who was now living in the Dark and feasts on blood and flesh. She and Alice went to a lot of different domains of different gods in the Dark. Thorne betrayed Alice at one point, selling her out to Morwena and Betsy Gammon. Thorne then redeems herself afterwards, helping Alice escape and killing Betsy Gammon. Thorne then attempted to kill herself afterwards, distraught with grief. Thorne believed herself to have failed Grimalkin, and to be an embarassment. She broke down in tears, and only stopped when Alice told her that Grimalkin was not humiliated or angered by her death, but greatly saddened. When Alice and Thorne were being captured by the dead witches Bony Lizzie and Mother Malkin and the abhuman Tusk and the demon Beelzebub, Thorne killed Tusk and cut off Beelzebub's thumbs which made Thorne get her thumbs back. She also killed Raknid with the Dolorous blade after Alice threw it to her.