Erised

"The Philosopher's Stone was not safe at Hogwarts. Minerva was sure of this fact, had been sure of it since Albus had asked her for her help in protecting it. Albus Dumbledore did not need help from her in guarding the Philosopher's Stone from You-Know-Who's followers; she knew that." What she wants to know is why. McGonagall-centric one-shot.