Secret Keeper Change

'Harry,' said Lupin hurriedly, 'don't you see? All this time we've thought Sirius betrayed your parents, and Peter tracked him down - but it was the other way around, don't you see? Peter betrayed your mother and father - Sirius tracked Peter down -
'That's not true! He was their secret keeper! He said so before you turned up, he said he killed them!'
'Harry... I as good as killed them,' Black croaked. 'I persuaded Lily and James to change to Peter at the last moment, persuaded them to use him as Secret Keeper instead of me... I'm to blame, I know it... the night they died, I'd arranged to check on Peter, make sure he was still safe, but when I arrived at this hiding place, he'd gone. yet there was no sign of a struggle. It didn't feel right. I was scared. I set out for your parents' house straight away. And when I saw their house, destroyed, and their bodies - I realised what Peter must have done. What I'd done.'

THE SERVANT OF LORD VOLDEMORT - Pg 389

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'Lily and James only made you Secret Keeper because I suggested it. I thought it was the perfect plan... a bluff... Voldemort would be sure to come after me, would never dream they'd use a weak, talent-less thing like you... it must have been the finest moment of your miserable life, telling Voldemort you could hand him the Potters.'

THE SERVANT OF LORD VOLDEMORT - Pg 392