This story starts after the Triwizard Tournament. There is a new Defence against the Dark Arts teacher (Vellum) who shows them the soakstone of Hogwarts (one of the keys) that soaks up all energy thrown at him. She offers fencing lessons and Harry starts to see Parvati.
In a fake duel between Vellum and Harry she steals his magical powers but he remains some and becomes the last mage. To learn more about this forbidden ’subhuman‘ tribe he visits Lucas the only other Mage who is imprissiond for this crime in Azkaban. Harry and Parvati split up because Cho and Harry are not in their dorms at night. Harry drains the Hogwarts key. Before chirsmas Parvati and Hermione are abduced by Wormtail with the help of Sprout. The remaining fifth year Griffindors and Cho man a rescueteam. On their mission Seamus is attacked by a werwolf. Dean transforms to defy it. Both are seriously injured and Ron takes them back (Lavender, Neville and Ginny stayed at the portal in Hogwarts). Cho and Harry manage to rescue them but have to get back via Azkaban. Returning they find out that Ron was killed. In the ensuing investigation it gets out that Harry is a Mage.
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The story is not available online, but there is still the PDF available.