I was just watching re-runs of Highlander and saw the episode about the Methuselah Stone and thought it could be a great crossover with HP.

The only guidelines to this challenge is that Voldemort must come searching for the Methuselah Stone and the Order comes to protect it. Immortals cant be known by the public of the wizarding world, but wizards such as dumbledore and voldemort might know about them.

Methos must be part of the story. He must be a wizard but he can not be Slytherin or Merlin.