The most troubling storyline in season one is the abusive relationship between Elle and Campbell. Sam, Campbell's brother, tells a highly disturbing story about how their parents had Campbell tested when he was a kid and he's a legitimate psychopath (one who gleefully and graphically murdered their pet bird). Unfortunately, Campbell takes a shine to Elle right off the bat, telling her she's pretty and that they're "the same" (i.e. loners with a darkness to them).
Even though he repeatedly vows to never hurt her, we see him do everything from hold her head underwater in the bathtub to leaving her with dark bruises and deep cuts all over her body from his physical abuse. She attempts to escape his hold over her by poisoning him on Thanksgiving, but that backfires when the pie she tainted ends up eaten by a bunch of other classmates and she's left with even more guilt to shoulder.
By the end of the season Elle almost makes it out of the relationship thanks to Allie and Helena's protection, but her efforts are thwarted when Campbell and Harry overthrow the "government" set up by Allie. Campbell drags Elle back to their home under the impression that Allie had imprisoned Elle, so he doesn't hurt her (at least not that we see). But the final shot of Elle makes it clear that she's not done fighting — not by a long shot.