If any of them were to join the Dark side, it should not have been him. Sirius had been born for it, circumstance should have pushed Remus into it, and James, with his wife and newborn son, had everything in the world to live for.
Peter had wanted to save them. He had tried.
He approached Sirius first. He had seen him at the last battle, had not missed how poorly Sirius had dueled, had known why.
"Regulus was there, wasn't he? He was one of the Death Eaters behind the masks?" Said Peter, finding Sirius alone in his flat. He had a bottle of firewhiskey in one hand, and the Daily Prophet in the other. The headline: DEATH EATER BLANCHE COLE KILLED BY AURORS, THORFINN ROWLE SENTENCED TO LIFE IN AZKABAN.
Sirius nodded, his jaw set in a hard line. They both knew the last three Death Eaters had not escaped out of sheer luck.
"I had to do it Peter." He whispered. "They were so outnumbered by the end. He would have faced life imprisonment if he were captured. I couldn't let my brother go to Azkaban, could I?"
They both fell silent.
"Do you ever want to join them?" Peter asked.
"I wanted to once." Replied Sirius. "Before I had come to Hogwarts, before I met you and Remus and James. Voldemort was just rising to power at the time. I remember that summer – I couldn't have been more than nine or ten at the time – Bellatrix and her family had come over for dinner. She told us about the Death Eaters, and it had sounded so exciting. Dueling and saving the world. Being a part of something. Maybe even making my family proud."
Peter heard the wistfulness in his tone and allowed himself to hope. He had wanted it once – was it so far-fetched that he should want it again?
Sirius shook his head. "Well, I'm doing all of that now. Except I have a different family now."
"Oh." Peter replied, and he could not keep the sadness out of his voice.
Sirius mistook the cause and clapped him on the back. "Don't worry Peter. We'll always have your back."
...
He had gone to Remus next. Remus, who met with nothing but contempt from their own side, and who had nothing to look forward to under the current order.
"Have you ever wondered what things would be like if the Dark Lord won?" Peter had said to him one morning after a difficult full moon. They were alone, just the two of them. Sirius had been called away on last minute Order business and James had been occupied with his son, so for the first time, it had been up to Peter to keep Remus company. And he knew if there was ever to be a time to save Remus, it was then, for Remus was at his most vulnerable. Disillusioned with the world, where people saw him as a vicious beast instead of a man, he had become more and more withdrawn – even from his own friends.
"Yes." Remus replied bitterly, as he dabbed dittany on one of his wounds. "I've wondered what it would be like if I joined him."
"The other werewolves have," said Peter. "The Dark Lord wants them in his ranks."
"He has promised prey. And a future in which we would no longer have to be outcasts."
Peter knew him well enough to know that it was longing burning in his eyes. It was the same look he had always worn before giving in to another one of James and Sirius's ill-fated schemes.
"Why don't you join him?" He asked. "Why risk your life for people who won't even look at you?
That light faded. "Because of you I suppose. You and Sirius and James." And he smiled. Because in a world of trial and temptation, it was the people who had stuck with you that made resistance worthwhile.
...
They asked him to be Secret Keeper. It was one thing to give information to the Dark Lord, but another to condemn his friends to certain death.
He visited them the evening after the McKinnons' deaths. They had died on his information – Marlene who used to bring homemade cookies to their Order meetings, Claudius who had lost a leg, their two children – Felix and Hortensia who had been so looking forward to attending Hogwarts. They were dead and he had done it, and if he didn't do something soon, Lily and James and little Harry would all be dead too.
So he went to Godric's Hollow that evening, was greeted by Lily who pulled him into a tight hug and told him how glad she was that he was alright, how grateful they were that he was their Secret Keeper.
He was unable to meet James' eyes, James who had given him friendship, who used to stay up late into the night to help him with his homework, who had refused to give up on him when it had seemed impossible that he should become an Animagus.
"I'm scared." James confessed to him when they were alone. "After what happened to the McKinnons… Imagine if it had been Lily and Harry. I wish there was anything I could do to keep them safe."
"Haven't you been tempted to join him?" Peter blurted out, unable to stop himself. "He would want you – you're pureblood, and talented; Lily's Muggleborn but he would make an exception for her. You wouldn't have to stay in hiding, you wouldn't have to worry about Harry, and he's taking over everywhere – is there any use in resisting?" Peter was afraid to look at his old friend, who was and had always been excessively noble and inconceivably brave, and who he was sure would never entertain a thought of joining the Dark Lord, but he did and was surprised to find that there was temptation in James's eyes, that his friend had not been insensitive to the many inducements the Dark side could bring for his family.
Peter thought, for the faintest moment, that he could convince him, that maybe, just maybe, the Potters would not have to die. But then they heard a laughing sound from little Harry, whom Lily was getting ready for bed, and James turned to the photos they had on the walls – of his parents waving gently, of the Order at their last meeting, of himself and Remus and Sirius and James on the last day of Hogwarts, laughing beneath the beech tree.
"But what good is it to live, if the world itself isn't worth living in?" James said at last, smiling sadly. "I know you're scared for us Peter. But don't worry, with you as our Secret Keeper, we'll be alright."