SLASH sets as its backdrop the combined worlds of high school and the niche corner of erotic same-sex fan fiction, known as "slash." Fan fiction is written by a fan of, and featuring, characters from, books, movies, and TV shows. Fifteen-year-old Neil (Michael Johnston) adds throbbing sexual encounters to his fan fiction, which he secretly scribbles in his notebook. The notebook is passed around by bullies at school, outing his secret. Neil is concerned that he might be gay, another secret that makes the shy and cautious boy feel uncomfortable among his high school peers. When he meets the far-more-experienced and outgoing 16-year-old Julia (Hannah Marks), his world changes. She brings to him adventure -- drugs, sex -- and pushes him to claim he's 18 on a website where he can publish his material and enter it into a fan fiction porn contest. She drives him to Comic Con, where he's invited to read his story about Vanguard, a pansexual outer space super hero. At Comic Con, Neil connects with Denis (Michael Ian Black), a 38-year-old writer and online fan. After taking MDMA, Neil has sex with Julia, but when she downplays the importance of their connection the next day, Neil tries to kiss Denis, seemingly on a mission of self discovery -- if Julia rejected him, maybe he's gay. Denis recognizes that the baby-faced Neil is underage and says no, but against the rules he lets the underage boy read his erotica at the fan fiction gathering. It's clear that Julia remains the troubled product of her broken home and Neil, from supportive and kind parents, struggles in his own way with growing up. Denis suggests that Neil isn't gay but just wants to be, in order "to fit in, somewhere small," because trying to fit in with the larger world would be too daunting.