Marcia Gay Harden made her brief debut as Sam Keating’s sister on “How to Get Away With Murder’s” Jan. 29 midseason finale, and on Thursday’s episode, she’ll come face-to-face with her dead husband’s wife, Annalise (Viola Davis), who’s concealing his murder — except, Hannah Keating doesn’t know that he’s dead.

“She’s in town to discover — not necessarily avenge — but to discover what’s going on with her brother,” Harden tells Variety of her recurring character, Hannah. “He’s just been accused of being a murderer by Annalise, which Hannah is aware of. She watches the news, she reads the paper. There’s nothing that’s typical from Annalise and so, she’s come down to figure things out — to right this wrong.”

Harden tells Variety what to expect from Hannah, plus, teases a major game-changer:

So Hannah really thinks that Sam is just missing — not dead?

I believe she just thinks he’s missing. She thinks he will show back up. It doesn’t make sense. These things are so extraordinary and so bizarre. The Keating Five and Annalise are near to the extraordinary more than the lay person because they’re in the world of murder, they’re taking a class of how to get away with murder, they’re discovering all kinds of cases, she’s a defense attorney. But to those of us who aren’t in that world, it’s pretty extraordinary, and those kind of accusations and that kind of behavior, it just seems unbelievable, so I wouldn’t make the case that she would come down there being suspicious. You’d expect that there’s a logical explanation and he’s going to turn up, until you put this story together.

Is that why Hannah came to town — to piece together Sam’s disappearance, rather than to come after Annalise?

Her arrival, to me, seems very normal. A sister would show up to defend her brother, and he’s missing. It just doesn’t sit right, it doesn’t feel right, it doesn’t make sense, and that’s what she’s going to town responding to. She’s a smart cookie. Her first job is to put the story together, to start connect the dots and to implore Annalise to help her put this story together.

How about the other murder? Hannah is aware that Annalise has accused Sam of killing Lila, but when Hannah made her debut last week, she told the police he’s not a killer.

It’s shocking when someone accuses somebody that you know of any kind of a heinous crime and I think that we all believe the best of people that we know — about our neighbors, about anybody.

As Hannah begins to piece together the story, do her motives change?

Yes, in some way. I think what she discovers makes Hannah more reckless, and I think that when you’re dealing with accusations and information on this level, you do not want to be reckless. I do think it changed her.

Is Hannah suspicious of Annalise in any way?

Why would she suspect Annalise? It’s very exciting to me that what the audience knows and what Hannah knows are two very different things. The audience already knows that Annalise knows about Wes, but here I am, the innocent lamb in the lion’s mouth. You know that there is no way that Annalise is innocent. She’s the mastermind behind his disappearance. But I don’t know that, so it’s kind of an intriguing test for the audience. I’m a lamb headed to the slaughter on some levels.

It sounds like you’re initially there for answers about Sam, and not out for blood with Annalise, but will that change?

I would say that we start working together, and then we work against each other.

How would you describe Hannah and Annalise’s relationship?

From what I understand from their history, Annalise has one perspective that may be completely different from Hannah’s. It could be class-based that Annalise came from a different class than where Sam and Hannah came from, it could be race-based, it could be behavior-based. Racial questions or racial issues between us, that doesn’t resonate for me. For Viola, it did resonate. For me and my background where I’ve lived, I didn’t have that problem, but what does resonate is moral codes. Hannah might have been very judgmental of the way Sam and Annalise broke their moral code, their marriage code, their marriage bond. There’s kind of a weird protecting that goes on with Hannah for Sam.

Viola Davis told Variety that Hannah was never accepting of Annalise marrying her brother. Why is that?

That’s an interesting thing. It’s like oil and vinegar, but neither one knows that they’ll repel the other until they’re in the salad shaker together, and you could even shake it up for a while and it seems to be one seemingly delicious blend of salad dressing, until you let it sit there and they settle back to their proper emotions.

Viola described Hannah as the “wrench” in her plan. Will she wreak havoc?

That would assume that she would even know what her plan is. All I know is that Hannah showed up and asked for truth. She doesn’t want to play games, she doesn’t want to be a part of a chess match, she just wants the truth.

In the sneak peek of your first major episode, it doesn’t quite seem like Hannah and Annalise see eye-to-eye. What can we expect between the two ladies?

What the conversation becomes is very personal between the two ladies. Part of the goal for bringing the character Hannah into the show is to reveal a bit about Annalise’s background, a bit about her life, a bit about why she is the way she is. My character showing up forces a kind of a reckoning, kind of a vulnerability for Annalise.

Can you tease anything else about your episodes?

At the end of this scene that we have toward the end of the episode [Feb. 5], there’s just this shocking bit of information that’s revealed and it changes everything.

Information about Annalise’s background or something else?

Something else.

Something having to do with Sam?

It could be!