Gaby Hoffman

Last season, Girls blew our minds with Booth Jonathan's video tower of terror. But this year, Gaby Hoffman has stolen the spotlight with her portrayal of Adam's sister Caroline. (And she didn't even need Duncan Shiek to do it.)

Caroline's the type of woman who breaks glass in her bare hands and tries to euthanize her own grandmother. But in her rare moments of calm, it's clear she possesses the same depth of wit and understanding as Adam (Adam Driver). She just doesn't quite know how to express it. Though frankly, neither does he.

"I think she is really struggling internally," Hoffmann tells TVGuide.com. "Whether it's because she has something like Borderline Personality Disorder or if it's because she's just in a lot of pain that she doesn't know how to deal with, I'm not sure. I'm not willing to really decide yet."

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Whatever is the catalyst of Caroline's struggle, her behavior shines a light on how Adam became the man who seamlessly switches from making you crawl on the floor like his own personal Secretary to sweeping you up in his arms like a regular Tom Hanks

After being forced to take care of Caroline his whole life, Adam still struggles to break free from his role of caretaker. And luckily for Hannah (Lena Dunham), this means Adam has a very high tolerance for her bulls---. "As far as Adam is concerned, [Hannah and Caroline] both need a lot from him ... This could be why he's drawn to [Hannah] in the first place," Hoffmann says. "We repeat our habits and our proclivities even if they're ones that we're trying to escape.

"I think that they had some troubles in their childhood that neither of them have properly dealt with and certainly have not expressed, at least to us as an audience," she explains. "And I also think that's what young adults are contending with more than anything, sort of unpacking their childhood and discovering the ways in which it's inhibiting them in their adult life."

The longer Caroline stays at Adam and Hannah's, the more details regarding their twisted relationship will be revealed. So just how weird does it get? "I think that they have a relationship that's more akin to lovers than brother and sister," Hoffmann teases. This slightly too-close-for-comfort aspect of Caroline and Adam's relationship will be dealt with head-on in the Feb. 1 episode. (But don't worry, the siblings never actually went full-on Flowers in the Attic.)

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In the meantime, Caroline will spend some quality time with Hannah on Sunday's episode when Hannah struggles to deal with a death in her life. Though — unsurprisingly — Caroline isn't the best person to provide guidance. "I think that Caroline is highly, highly manipulative," Hoffmann says of the pair's time together."I think she likes to test people and play with people."

But while Caroline's version of "entertainment" verges on psychotic, she might be more similar to Hannah than the struggling writer would like to admit. Sunday's episode sets up a frightful parallel of what Hannah's own detachment could turn her into if she doesn't learn to think outside herself.

"[Caroline's] almost a warning," Hoffman says. "It seems almost like a foreshadowing of what can happen to somebody who doesn't deal with their s--- and a kind of mental illness that can be the result of a blindness to themselves.

"Obviously, Hannah is a lot more stable and sane than Caroline in their respective moments in life," she says. "There is a narcissism they both have. I think Hannah is much lighter and more charming in hers."

Girls airs Sundays at 10/9c on HBO. Do you think Hannah and Caroline are similar?