Harry couldn't believe it. He'd gone through each memory in the Pensieve five times, and the first one he'd gone through six. Each time, he took a different angle, and the result was always the same. Severus Snape had gone to his parents' house at Godric's Hollow to warn his parents of the impending attack, insisting that Sirius had betrayed them. Snape had veritably pleaded with his father to leave. He'd offered to hold Voldemort off for his father, at certain peril to his own life, but James, knowing that Sirius couldn't have betrayed them even if he'd wanted to, since he wasn't the Secret Keeper, had refused to listen to his old classmate, even when Snape had shown him his Dark Mark.
When James had realised it was too late, he'd sent Snape upstairs to escort Lily and Harry to a safe place, but Lily had also refused to listen, and so Snape had tried to take Voldemort down from under cover. It hadn't worked, of course, but it was Snape who took Harry to Dumbledore, and Dumbledore had taken him back to Godric's Hollow so that Hagrid could “find” him.
Snape had tried his level best to save his parents' lives, his parents had ignored him, and instead of trying to escape with his own life, he defended them until the end.
How wrong, how utterly, incomprehensibly, wrong, Harry had been about Snape.
How wrong was he still, he wondered.
Hermione and Ron had been watching in concerned silence as his face stormed through many emotions while he tried to work things out in his mind. Resolved, he looked at his two friends for a few moments. “Do you two mind leaving me alone for just a few minutes?” Harry asked politely.
“Of course not,” Hermione said, standing, and levelling another glance at Dumbledore's portrait. The old wizard's eyes twinkled.
“Come on, Ron,” Hermione said, “we'll be just downstairs, Harry,” she informed him, pulling the door shut securely behind her.
Harry looked at the portrait of Albus Dumbledore. “How did he know where the house was, if he wasn't the Secret Keeper?” In his tumultuous emotions, he neglected to clarify who “he” was.
No matter, Dumbledore knew.
“He overheard who he thought was Sirius Black telling Voldemort. He was hidden under the Invisibility Cloak and nobody knew he was eavesdropping on that meeting. Having heard the address directly from what we now know to be Peter’s mouth, he Apparated directly there to try to warn your parents.”
“What was in that potion in the basin?” he demanded next.
“Hm. Well, I am not actually the person to answer that, not having been the one who made it. Suffice it to say, it was killing me. As was the curse on the ring.”
Harry looked back and forth across Dumbledore's portrait, considering this, and crossed his arms and feet in thought as he leaned back in the chair. He tapped his right foot relentlessly. “Were you pleading for your life?” he asked next.
“I would never plead for my life, Harry, but especially not when a long and very assuredly painful and inevitable death awaited me, even if my dying wouldn't have assured my key spy's place in the movement.”
“Be careful, Harry . . . in what you say, and what you do. It would be best if you not share this with anyone, I believe.”
“I will be careful, and I won’t tell anyone, not even Ron and Hermione,” the younger man said. Pausing to reconsider, he said, “Well, at least, not anyone who doesn’t already know,” and with a determined look, swept from the office.
Dumbledore’s portrait heard Harry ask, and Ron reply: “Ron! Can I borrow Pig?”