Regulus knocked on the door politely and awaited McGonagall's voice before he let himself in. He quietly shut the door behind him and entered the room. "Hello Professor," He said almost ashamedly. It was not too long ago that he was preparing for Newt's in her class.
"I know how to defeat Voldemort," Regulus started the conversation plainly. He went on sort of rambling honestly. McGonagall wasn't really responding, and so Regulus kept talking, about how he found out about the locket from Voldemort requesting to use Kreacher, and how he left him to die at this cave, and then how Regulus finally came to realize Voldemort was a power hungry, immortal seeking dictator. And then he went on to tell her how he discovered that it was a horcrux and how he couldn't die because his soul was saved into the locket. That he had tried to drink the same substance that Kreature had to drink, so he could send the house elf off to destroy the locket, but the explosion had kept him from doing so and that the house elf had died saving him. Regulus' voice retained a bit of sadness at that part. "I know that I'm not exactly someone you should believe but-" Regulus didn't know what to say. Because he had no excuse for his past choices.
McGonagall had looked a bit alarmed at all of the information. She had padded up to him and placed a hand on his shoulder. "Is the locket the only one?"
Regulus looked up to her, he didn't know. But it took a lot off his chest to know that she at least considered all that he said to be possibly true. But It hadn't occurred to him that there could have been more than one. "I-I don't know."
McGonagall went on to explain to him that he was welcome to stay, but not to be surprised that he would have an eye kept on him.
Regulus graciously declined her offer, "I'm sorry ma'am but I don't think it's safe for anyone if I remain here."
She nodded, and told him he's welcome to come back. McGonagall said that she had to go talk to the proper people about his news and turned and opened the door to let them both out.