Harry Potter and the Lively Hallows

Begins right before Albus Dumbledore's death in The Half Blood Prince. What if Draco Malfoy had been the one to pull the trigger? What if Draco Malfoy had assassinated the great Albus Dumbledore? How does this affect Harry Potter and his actions? What will Severus Snape be forced to do, now that he has failed to fulfill his promise to Dumbledore.