The characters of Sleepy Hollow will have to contend with enemies of both supernatural and Revolutionary War origins in tonight's episode, "The Lesser Key of Solomon."

Facing off with demonic forces is becoming the norm for Ichabod Crane (Tom Mison) and Lieutenant Abbie Mills (Nicole Beharie). Now the duo will be attempting to keep a group of Hessians - German mercenaries who aided the British during the Revolution - from unleashing 72 condemned souls.

Unfortunately, this plan somehow includes Abbie's sister, Jenny, who has recently escaped from the mental institution. However, the Mills sisters are not necessarily on the best of terms, a fact that complicates matters.

"They have sort of a caustic [relationship], they have a tough relationship and there's a lot of history there," Beharie said, according to Access Hollywood. "It's going to be really interesting to see how that unfolds and how Jenny plays into it, because she obviously knows some things."

While Abbie may not have the best of relationships with her sister, the police officer is becoming closer to Crane as their partnership develops. However, don't expect the pair to become an item.

"It's so excellent to start a show where the lead female is an independent character. She's not defined by the men that she's around," Mison said of Beharie's character, according to Crave Online. "That's one of the things that drew me to it is it's so classy to have a female lead like that who's her own and she's rounded, she's clear, she has missions rather than being the love interest or the mother or the daughter. I think that was a classy choice."

In the meantime, Crane will lend a bit of historical perspective to the investigation, revealing that the Boston Tea party was actually a cover for the colonists to steal something from the British.

Even though the Fox series is only entering its fourth episode, the genre-bending program has already been picked up for a second season.

"The show has proven to be a risk well worth taking - it's a conceptual blast unlike anything else on television and it all holds together with inventive writing and a fantastic cast," said Kevin Reilly, Fox Chairman of Entertainment, according to Spoiler TV. "I can't wait for fans to experience what else is in store for this fall and even more of this wild ride into Season Two."

Sleepy Hollow airs Mondays at 9 p.m. on Fox.

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