Asked to describe Annalise and her sister-in-law Hannah's relationship on How to Get Away With Murder, Marcia Gay Harden comes up with one concise sound bite: "They're cut from the same cloth even though they're different manufacturers."

Annalise (Viola Davis) has seemingly met her match — and perhaps her Achilles' heel — in Hannah (Harden), who is going to throw a big wrench into Annalise's plan to get away with her husband Sam's (Tom Verica) murder and pinning Lila's murder on him. "Whatever his wife told you, my brother is no murderer," Hannah told police in the closing seconds of last week's episode. On Thursday's episode (10/9c, ABC), Hannah will start her own investigation to get to the bottom of her brother's "disappearance," much to Annalise's chagrin.

How to Get Away with Murder postmortem: Annalise is "playing many sides at once"

"I don't know if she thinks [Annalise] killed Sam. She's trying to connect the dots and things just don't make sense. The idea of people that you know as murderers is completely bizarre," Harden tells "But she's not afraid of her. She's not afraid to go toe-to-toe with Annalise. She's not a student. She's not younger than her. ... They're two ladies who come from very different backgrounds, have very different stories of wealth, education, etc. They're in some ways similar to each other — they're very tough and never really suffered each other's friendships."

Adds executive producer Pete Nowalk: "No one has faced off with Annalise the way Hannah has. They have a very rocky history and she really is the first person we'll see who's not scared to stand up to her and call her out."

Part of that dynamic is a consequence of Hannah never having accepted Annalise from the beginning, Harden believes. Though the writers gave the Oscar-winner tidbits about Hannah — upper-middle class, educated, single, psychiatrist — Harden crafted much of Hannah's backstory herself, including that she didn't like how Annalise came into Sam's, and thus her, life: as his mistress. "She had an affair with Sam and I obviously knew the first wife, and [Annalise] and I just never saw eye-to-eye on anything," Harden says. "We operate very differently. She's very closed. I'm very seemingly open. Hannah doesn't like secrets and Annalise is very comfortable with secrets."

"Secrets" is the crux of Annalise and Hannah's relationship. Working off what writers told them — "We sat down and I said, 'Tell me everything!' And they said, 'Well, we're discovering it too!" I said, 'OK!'" Harden says with a laugh — Harden and Davis got together to discuss their characters' contentious history, ultimately landing on a character study. "There's this tension that people just aren't themselves. Viola was curious about, as everyone is, with these issues: Is race a factor?" Harden says. "If it was, how much of it was a factor? If not, what does that say? Or is it a factor for [Annalise] but not for [Hannah]? What do we project onto certain situations? What do we project onto certain people? Someone can go into a room and say, 'I felt like I stood out. I'm the only white girl.' Somebody else could say, 'We didn't care!' Some of this could've been coming from her."

6 teases for How to Get Away with Murder's return

Like perhaps an inferiority complex? Annalise has been an imposing figure in and out of court, but would she cower to someone like Hannah? Even if she does, Harden's not so sure of Annalise's intentions. "Someone can feel inferior without the other person thinking they're inferior. Each of us has our own idiosyncrasies that would lead to dysfunction. I think she's brilliant and I think my character thinks Annalise is brilliant and tough and rough and standoffish," she says. "You see [Annalise] break down, but then you question whether it's manipulation or not, like with Wes [Alfred Enoch]. With Hannah, it's more about history, although with Annalise, I don't think you ever know if she's telling the truth or not. Having watched the episodes, my feeling is just you never know with this lady! Even her most sincere crying could be manipulative. You just don't know."

Harden will only appear in three episodes, but she promises Hannah will "leave her mark." "Next week's episode is about connecting all the dots," she says, before teasing of Hannah's exit, "All I can say is that the police get involved."

How to Get Away With Murder airs Thursdays at 10/9c on ABC. Check out a sneak peek of Thursday's episode below.