As CBS’ Elementary resumes its second season this Thursday at 10/9c, Sherlock’s biggest foe — and love — is back, and with a whopper of a secret.

But first, there’s a case to be solved that may have ties to the (imprisoned?) Moriarty, played by guest star Natalie Dormer (Game of Thrones). What’s more, the P.I. that Sherlock once knew as Irene Adler has a newfound fascination with his partner Joan, executive producer Rob Doherty previews.

Read on to find out what Joan will make of the former lovers’ covert correspondence and why she’s on Moriarty’s mind.

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TVLINE | What brings Moriarty back into Sherlock and Watson’s lives?

A young girl is kidnapped in New York City and Sherlock and Joan quickly come to believe that Moriarty may have had a hand in the abduction. With Captain Gregson’s help, they track her down and pull her into the investigation.

TVLINE | So she’s not still in prison?

Oh, that’s a complicated answer. [Laughs] She is still in federal custody. She has been in federal custody since the events of last year’s finale, but she is… well, Moriarty would not necessarily let incarceration keep her from pulling certain strings.

TVLINE | Is Moriarty any different considering everything that’s happened since last we saw her?

She’s incrementally more humble for having lost to Sherlock and Joan at the end of the first season. It’s something she’s had a little time to chew on and puzzle over. She still doesn’t quite get it, doesn’t quite understand that Sherlock and Joan as a unit are more than one Moriarty. But she’s a student even of her own mistakes, so she takes this opportunity to dig a little deeper into Sherlock and Joan’s relationship and try to figure out, first and foremost, where she went wrong and second, what that relationship is really about.

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TVLINE | They bested her, so that’s got to sting when she sees them again.

It’s tricky. [Laughs] From the very beginning, it will be very clear that Joan, in particular, has been on Moriarty’s mind.

TVLINE | Yes, why does she have a painting of Joan?

We established that one of her many talents is painting. She may be a very devious personality, but she has some artist talents. The painting announces pretty quickly to the audience that she’s been thinking about Joan.

TVLINE | On the other end of this equation, there’s Sherlock and Joan. How does Moriarty’s presence affect them?

We established earlier in the season that Sherlock was participating in a secret correspondence with Moriarty. We showed that the two of them had been exchanging letters. In this episode, when Sherlock realizes the two of them are going to have to see Moriarty, he knows there’s no point in keeping it from Joan any longer. And so it’s a lot for [Joan] to digest as the story begins. It’s a little surprising, a little confusing, at first and yet, over the course of the episode, she’s starts to understand Sherlock, for all his quirks, is still a guy with a broken heart…. But it doesn’t make it easier for Joan to be in the same room with this woman. They certainly have plenty of unfinished business between them, but we’re going to learn a lot more about Moriarty in this episode. We’re not completely pulling the curtain away, but I can guarantee at least one big secret about Moriarty and her past will come to light.

TVLINE | Is she a presence that you hope will recur throughout the season?

Gosh, it’s always so hard to say. If I had my druthers, she would absolutely be a recurring presence over the life of the series. It’s harder to say if we’ll see her again this season only because Natalie is an incredible actress and in demand for very good reasons. And so sometimes, it can be tricky to make sure schedules mesh in our favor. So absolutely, we cannot get enough of Natalie and would love to have her back, but it’s too soon to say if that would happen again this season.