Supernatural will reevaluate the Mark of Cain during the season 10 fall finale.

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Titled "The Things We Left Behind," the Dec. 9 episode will put Dean's little problem back on the table, reintroduce Claire Novak, mention John Winchester, and potentially deal with Castiel's failing grace - all while leading up to a twist.

Dean's Mark of Cain reared it's ugly head once more in "Ask Jeeves," and TV Line reports that the elder Winchester will finally make a decision about Cain's little gift before heading into the winter hiatus. He will have to do so while chasing around a teenage Claire Novak, however, because the daughter of Cas' vessel will leave Team Free Will high and dry after they spring her from a group home.

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While director Guy Norman Bee ("Stairway to Heaven," "Devil May Care") describes The Things We Left Behind" as an "odd" episode, Outsiders writer and Supernatural fan S.E. Hinton also dropped a few teasers from set.

"Dean told Cas a favorite story about his Dad, John Winchester," Hinton tweeted in October. "Both bro said they loved their Dad ver[y] much. Sweet scene."

The author also hinted at an important conversation between the Winchester brothers.

"Short sweet scene in morning with Sam & dean, old fashioned bro scene," Hinton teased. "U will love it."

Sounds like the fall finale will leave fans with plenty to talk about. Are you looking forward to "The Things We Left Behind"? Sound off in the comments below.

Supernatural airs Tuesdays at 9 p.m. ET on The CW. Click the video below to see a preview for the series' next episode, "Girls, Girls, Girls."