Por que Remus não foi informado de que o Secret Keeper foi alterado?

Isso é discutido por Remus e Sirius quando Peter implorou que eles não o matassem na Casa dos Gritos no final do Prisioneiro de Azkaban . A razão era que eles não sabiam quem era o espião e Remus era um suspeito.

“Remus!” Pettigrew squeaked, turning to Lupin instead, writhing imploringly in front of him. “You don’t believe this ... wouldn’t Sirius have told you they’d changed the plan?”

“Not if he thought I was the spy, Peter,” said Lupin. “I assume that’s why you didn’t tell me, Sirius?” he said casually over Pettigrew’s head.

“Forgive me, Remus,” said Black.

“Not at all, Padfoot, old friend,” said Lupin, who was now rolling up his sleeves. “And will you, in turn, forgive me for believing you were the spy?”

“Of course,” said Black, and the ghost of a grin flitted across his gaunt face. He, too, began rolling up his sleeves. “Shall we kill him together?”

Assim, a razão para não dizer a Remus era deliberada (eles não confiavam nele) e não que eles simplesmente não tivessem tempo para contar a ele (como outra resposta sugere). De fato, sabemos de Prisioneiro de Azkaban Capítulo 10 que havia pelo menos uma semana inteira entre o desempenho do Feitiço de Fidelius e as mortes dos Potter:

“But James Potter insisted on using Black?”

“He did,” said Fudge heavily. “And then, barely a week after the Fidelius Charm had been performed — ”

“Black betrayed them?” breathed Madam Rosmerta.

“He did indeed.

Na época em que Sirius deveria se tornar o guardião secreto, ele os persuadiu no último minuto a mudar para Peter.

He was pointing at Black, who shook his head slowly; the sunken eyes were suddenly overbright. “Harry . . . I as good as killed them,” he 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 his 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 realized what Peter must’ve done . . . what I’d done. . . .”

_{Harry Potter and the Prisoner of Azkaban, Chapter 19}

Isso foi feito por Sirius na crença de que Bluffing Voldemort e seus seguidores iriam atrás de Sirius como uma opção melhor, sem saber que Peter já havia se vendido para Voldemort.

“Lily and James only made you Secret-Keeper because I suggested it,” Black hissed, so venomously that Pettigrew took a step backward. “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, talentless thing like you. . . . It must have been the finest moment of your miserable life, telling Voldemort you could hand him the Potters.”

_{Harry Potter and the Prisoner of Azkaban, Chapter 19}

Então, basicamente, os únicos que sabiam eram os que estavam lá. Peter traiu os Potters para Voldemort, e fez a sua fuga logo depois que os Potters foram mortos quando Sirius veio para ele. Depois disso, Sirius estava em fuga e acreditava ser responsável, e o único a contradizê-lo aparentemente estava morto.

“Just before he transformed,” said Black. “When I cornered him, he yelled for the whole street to hear that I’d betrayed Lily and James. Then, before I could curse him, he blew apart the street with the wand behind his back, killed everyone within twenty feet of himself — and sped down into the sewer with the other rats. . . ."

_{Harry Potter and the Prisoner of Azkaban, Chapter 19}