Lost Girl follows supernatural seductress Bo, a Succubus who feeds on the sexual energy (sometimes called "chi") of humans. Growing up with human parents, Bo had no reason to believe she was anything other than the girl next door - until she drained her boyfriend to death in their first sexual encounter. After years of running, Bo discovered she was Fae, creatures of legend and folklore, who pass as humans while feeding off them secretly and in different ways, as they have for millennia. Relieved to find out that she is not alone, yet horrified, Bo decides to take the middle path between the humans and the Fae while embarking on a personal mission to unlock the secrets of her origin.
With the help of her sidekick, Kenzi, local Fae wisemanTrick and her on-again/off-again love interests, Dyson and Lauren, Bo's journeys into the world of the Fae is met with danger at every turn.