The relationship between besties Stefan (Paul Wesley) and Caroline (Candice Accola) is built on their shared desire to stay good despite their vampirism. The two became friends when Stefan coached newbie vampire Caroline through her bloodlust. He kept her from going on a classmate killing spree, and since then, Caroline has done the same for Stefan. But is that all about to change? Will these two moral vampires kill in the Season 5 finale?

This season, the Steroline friendship has continued to operate around the characters’ respective choices to kill or not kill. For Caroline, she was told by the Travelers that, in order to prevent Stefan’s death, she would have to kill his doppelganger, Tom. Caroline traveled all the way to Atlanta to find Tom, but couldn’t do it. (Though Enzo did.) She confessed to Stefan: “I failed. I couldn’t kill him. Not even to save you.” He told her: “You do realize that you’re feeling guilty for not being able to kill somebody, right?” He said that he knew she “wouldn’t do it...because that’s what makes you you.”

In last week’s episode, the two shared a similar conversation except, this time, Stefan was the one who had been forced to face the dilemma of killing someone (Enzo) for someone he loved (Damon/Elena). Though Stefan didn’t actually kill Enzo -- Enzo killed himself by Stefan’s hand -- Stefan seems to believe himself guilty of the murder. He confided in Caroline that he didn’t tell her about Enzo’s death because “maybe I didn’t want you to know that I killed Enzo...I didn’t want you to think any less of me.”

Yes, these moments serve as important character beats within their respective episodes, but they also carry on a theme that could come to a climax in the Season 5 finale: will these characters choose to kill — in particular Caroline, who has been presented as the more moral of the two? We think so. And we think it might be for Stefan.

We’ve speculated before that something terrible happens to Stefan in the penultimate episode of Season 5. According to the synopsis for this week’s episode, “Caroline is witness to an unthinkable act of violence by one of the Travelers.” We think that unthinkable act will happen to Stefan, and it is going to send the entire crew into a tailspin for the season finale.

According to the Season 5 finale synopsis, “Heartbroken by an unexpected tragedy, Damon is focused on holding himself together.” And Elena and Caroline seem equally freaked out: “Elena takes matters into her own hands and demands that Liv and Luke help her, but Liv refuses to cooperate until Caroline provides her with some personal motivation.” Is that personal motivation threatening Luke’s life? And, if so, will Caroline actually go through with it? It is not usually how she operates, but “Liv’s off-hand remark regarding Stefan gets a surprisingly emotional response from Caroline.” If presented with the same choice the Travelers gave her before — kill someone to save Stefan — will Caroline choose differently this time?

Do you think Caroline or Stefan will kill in the Season 5 finale? Share your theories in the comments below!

The Vampire Diaries airs Thursday nights at 8 p.m. ET on The CW.

Kayti Burt is a contributing writer for Wetpaint Entertainment with a penchant for all things pop culture. Follow her on Twitter and Google+!