Harry Potter and the Prisoner of Azkaban
"You killed my parents," said Harry, his voice shaking slightly, but his wand hand quite steady.
Black stared up at him out of those sunken eyes.
I don't deny it," he said very quietly. "But if you knew the whole story."
"The whole story?" Harry repeated, a furious pounding in his ears. "You sold them to Voldemort. That's all I need to know." (17.104-107)
"NO!" Hermione screamed. "Harry, don't trust him, he's been helping Black get into the castle, he wants you dead too – he's a werewolf!"
There was a ringing silence. Everyone's eyes were now on Lupin, who looked remarkably calm, though rather pale.
"Not at all up to your usual standard, Hermione," he said. "Only one out of three, I'm afraid." (17.143-4)
Lupin's face hardened, and there was self-disgust in his voice. "All this year, I have ben battling with myself, wondering whether I should tell Dumbledore that Sirius was an Animagus. But I didn't do it. Why? Because I was too cowardly. It would have meant admitting that I'd betrayed his trust while I was at school, admitting that I'd led others along with me [...] and Dumbledore's trust has meant everything to me." (18.52)