Lily and James arrive late to their classroom following a mishap with a first year and a terribly done jelly legs curse, only to find it deserted and a message informing the class that their professor is sick and they now have a free period. Upon their return to the common room, they discover it empty too. Neither can be bothered to hunt out their friends – they're all probably halfway to Hogsmeade by now – so they flop down onto a couch, deciding to take advantage of the peace in the empty common room.

Later, after they have wiled the afternoon away talking about everything from Quidditch to life after Hogwarts, James asks Lily if he can kiss her. It might be the tiny goose bumps that prickle on her skin when his arm brushes against her leg, or it might be that their conversations about nothing of great importance have suddenly become so very important to her, or it might be the way his eyes seem to look right into her when he asks her, but for some reason she doesn't hesitate in saying yes.

She expects that with the utterance of that simple word, the world will stop turning on its axis, but all that happens is James' mouth opens almost imperceptibly in surprise and her cheeks tinge with red. Then he is leaning towards her, it all at once seeming to take weeks for his face to be next to hers, yet like no time has passed at all. He lingers for a moment, his face so close to hers that she can see the tiny smattering of freckles that sit just above his top lip and feel his hot, sweet breath against her lips.

And then James closes the miniscule gap between them, his nose nudging hers and reminding her to tilt her head slightly, a small nervous laugh escaping her lips as she does so. It is James' mouth that swallows her laugh as his lips finally slide over hers. Lily closes her eyes, her heart rate immediately quickening, both with excitement and terror as her mind registers how well his lips, chapped from too many windy Quidditch practices, seem to fit over hers.

James is gentle at first. He brushes his lips against Lily's softly and almost excruciatingly slowly, like he is afraid that anything more will scare her away, but then she lets out a small whimper, whilst at the same time lifting a hand and twisting her fingers into the soft material of his jumper. Suddenly he is bolder, moving his hand to the back of her head, his fingers tangling into her hair, his lips now firm and insistent on hers.

Lily's whimpers aren't small now; they are unashamedly tumbling out of her mouth, asking desperately for more and James is more than happy to respond. His mouth opens, his breath that tastes like the chocolate he scoffed as they chatted earlier mingling with hers. Then his tongue is running along the contours of her mouth, probing gently. Lily's lips part without her even thinking about it, like it is the most natural thing in the world and their tongues come together in an intoxicating, all-consuming dance.

Nothing has ever felt more right to Lily than this, than James' tongue, warm against hers, and his hand in her hair and the feel of his heart pounding in time with hers because his chest is now pressed against hers. It is all she can do to remember to breathe. It feels like a whole lifetime has passed before James pulls away, his teeth lightly grazing her bottom lip as he does.

As she takes in a great gasp of air Lily opens her eyes, bringing them up to meet James'. He is gazing at her with such intensity that she cannot help but gasp. It is a while before either of them can speak.

Years later, as Lily sits with Harry in his nursery and soothes him back to sleep, she remembers that day when her professor was sick and James first kissed her. She suddenly understands the fragility of the world; how the tiniest beat of a butterfly's wing, a minute, seemingly insignificant event, can alter something forever. She realises that if her professor hadn't been sick she might not be sitting here today, in this house where she hides, afraid for the life of herself and her family. But if she could, she wouldn't go back and change it for anything.