It's Dean-centric, pre-series, Stanford-era.
Jai Guru Deva Om
Feeling abandoned by his family, an emotionally vulnerable Dean investigates a strange commune alone. With Sam at Stanford and John off the grid, help seems unlikely when the young hunter falls under the influence of the group’s charismatic leader.
(Title and chapter titles taken from "Across the Universe" by the Beatles. You can find it on YouTube if you want)