Harry Potter and the Order of Merlin

There is an ancient Order out there far older than the Order of the Phoenix. What happens if Harry Potter is rescued by said knights? How will this change him? Change his world? Mentions of plural marriage, but none take place. Harry MOD long enough to help. No Sirius' will be hurt permanently in the making of this story. AU. A bit of Dumbledore bashing. I will repent of that.