Kat Graham and Persia White

What does a vampire do when he can't get the job done? Call on a witch.

As we last saw on The Vampire Diaries, Stefan Salvatore is looking to take Klaus down, but a locked coffin stands in his way. Bonnie's powers seem to be the only thing that can uncover the key to destroying the most dangerous hybrid in town.

"Stefan feels that it's so important to his freedom, it's detrimental to everything that he wants, to get [the coffin open] because he doesn't want to deal with Klaus anymore on any level," Kat Graham tells TVGuide.com. "He calls on Bonnie [who's] resistant at first like."

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But Bonnie doesn't just have decide if she should unlock the coffin. She's caught between Stefan's plea for help and best friend Elena, who strongly opposes Stefan's plans for revenge.

"How Elena is affected in all this really is very important to Bonnie [so] she's going to be weighing all the options. If she does [open the coffin], does she let Elena know? Does she not let Elena know? What would happen if she lets Elena know?" she says.

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Ironically, Bonnie's involvement with Stefan leads her to an important person in her life: her mother, Abby Bennett. "This leads her back to finding her mother who, we'll learn, left town 15 years ago, gave up her witchcraft and gave up her family," executive producer Julie Plec says. "[She'll be] reuniting and working out a lot of issues with her mother."

Graham adds that Abby's involvement in the mythology is "intriguing and shocking and important and you'll be surprised."

Watch this week's Vampire Diaries Bite for Graham's thoughts on a Bonnie-Jeremy reconciliation: