Prophecy Problem (One-Shot)

In the Hall of Prophecies something that none of the key-players had foreseen takes place, and the plans are permanently derailed as Harry becomes aware of not just the truth previously hidden, but a truth that came into existence solely because of the lies he has lived through already. Made aware of the many betrayals, he does what needs to be done. One-Shot, Dark!Harry, Dum!Bash