the silver lining - tmr

Apollo Rosier was what many would call a genius in the making. From the mere age of two and a half (be sure that it's two and a half, not three.), Apollo had been performing magic. Now, she would not necessarily call herself a prodigy, but she was aware enough to be confident in her own mind. The Rosier Heir knew she would absolutely be going to Hogwarts when she turned eleven, and even surer that she'd be placed in Salazar Slytherin's house. Where else would she go?

But little did Apollo Rosier know that her time at Hogwarts School of Witchcraft and Wizardry would be a lot more hectic than she'd expect, and all due to a brooding boy the same age as her, who she met that fateful day on the Express.

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Or, in which Tom Riddle met a girl who never would have existed in another universe on the Hogwarts Express, and his bleak future bled away like a forgotten nightmare.

on ao3 under the same name and user also!