Somewhere between 'Mates, aren't her eyes lovely? They look like the lush hills of Erin after a rainstorm…' and 'She's going to give me a whole brood of little Potters, just you wait!' Sirius had had enough. Lily Evans was finally giving James the time of day and the consequences for his mates were simply unacceptable. No bloody bird would be the reason Prongs wasn't spending time with his best friends!
So one morning early in November, Sirius snuck into Peter's four-poster and cast an imperturbable before roughly shaking the boy awake. 'Wormy! Wake up, mate!'
Peter's groggy eyes surveyed Sirius for all of a second before he groaned and tried to shove his friend off, to no avail. Sirius pinched Peter's arm and received an automatic smack in the face for his troubles.
'Wormy, fucking stop and listen! I've got an idea to bring Prongs back to us!' he hissed conspiratorially. Peter's eyes narrowed but he stopped fighting as Sirius pulled him to a sitting position.
'Fine, but if isn't worth me waking up at… bloody hell, what time is it, even?' The dorm was still dark, not even the sound of a mouse scurrying across the floor. Except of course Remus's legendary snore, and James's gurgling whine and giggles no doubt centred on a particular redhead.
'Doesn't matter!' Sirius replied, a gleam in his eyes. 'Listen, here's what we're gonna do…'
The second James sat next to Lily at the breakfast table a few days later, the Head Girl's eyes widened and she quickly clamped her nose, waving at something offensive that had apparently wafted over. James looked entirely clueless as the other surrounding Gryffindors simultaneously retched and groaned in disgust; some even got up, clutching their stomachs as they ran from the Great Hall.
Sirius shared a grin with Peter and an inconspicuous thumbs up across the table.
For the rest of the day, an awful stench clung to James. The combination rotten eggs/cabbage/dying animal smell had everyone running for their lives whenever the Head Boy was within a few yards. His eyebrows always shot up in shocked silence whenever the next person ran for cover. That brilliant bit of the prank was Wormtail's idea: making it so that the potion affected others, but the victim couldn't tell he reeked like months-old rubbish.
When Lily shook her head frantically and grimaced for the tenth time that day, James dejectedly retreated to the seventh year boys' dorm and flopped onto his bed, bemoaning his awful day. Sirius and Peter stifled their laughter as best as they could when they sat on either side of James on his four-poster. The counter-potion was working brilliantly; they couldn't smell anything but roses.
'Mate, it's all right. Y'know how it is: one day they love you, the next, they're breaking your heart,' Sirius said sympathetically, a hand rubbing large circles across James's back.
Peter patted the boy's shoulder and nodded sagely. 'Yeah, tough luck. But hey, we'll never leave you, right Padfoot?'
'Never! Marauders for life!'