It might take you a minute to realize why you just have a good feeling about that young man Charlie Manson in the early episodes of Aquarius. Yes, the show, which stars David Duchovny as a Los Angeles detective, meets Manson in 1967, before he became the infamous murderer we know today. But Manson is also played by Gethin Anthony, last seen by many audiences as the charming, doomed Renly Baratheon on Game of Thrones.

Thanks to theater training at L.A.M.D.A. and a list of credits that stretches all the way back to The Sound of Music as a child, Anthony knows how to transform himself for a part; but playing a notorious murderer required some extra preparation. He spoke with Vanity Fair’s executive West Coast editor Krista Smith about what it took to get into Manson’s head, what surprised him about the character, and the epic party he plans to D.J. for the Game of Thrones characters who are no longer with us.

VF Hollywood: I have really found myself wishing you were still on Game of Thrones this season.

Gethin Anthony: Yeah, well, thank you. It’s funny, this season’s story line of Brienne and sort of remembering Renly, I sort of feel a bit more a part of it than I have been the past couple of years; still feel his ghost is living on somehow.

Do you watch it still?

I did kind of a mini-binge to catch up. When you watch it intensely it really takes you to a dark place. I don’t know if this is just me, because I worked with some of those actors when they were younger, especially Sophie and Maisie. I very much remember them as children, and they are young women now—but seeing them go through tough scenes is really quite difficult, actually.

Yeah, I think I’m done. After that rape scene I like threw the clicker at the television and was like, “I’m out!” That’s my Sophie!

I saw that she seemed to be very excited about getting placed in those dark things, like in interviews. It’s tough for us, but as a young actress she’s getting to do some of the extraordinarily challenging work, and I remain blown away by the young actors, or all the actors on the show, especially the young ones.

Just make sure to invite me to the party for all the people that have been killed off.

I definitely, definitely think we should think about throwing that. I’d happily D.J. that party.

Were you surprised when you got the offer to play Charles Manson on Aquarius?

Yeah, I think on some level when you get an extraordinary opportunity and you make the best audition tapes that you can and all that, you want to believe. I think by that point I’d done so much work on the character that I was really hopeful that I would get a chance to pay that off and get to play him. [When I got the role] I think I stood outside a pub in London and just laid down in the middle of the street. I was just in a state of shock when I got the call.

How important is preparation for you in any role?

I feel most comfortable when there has been a huge amount of prep and a huge amount of getting to know the material, so that when you’re there in the moment doing it, especially on screen, you can just let it go. I really remember from, again, Game of Thrones’ second season, how much I wrote my own stories about what my character had been up to with Loras between the seasons.

With Manson that was all the more important. Our show [takes place] at a point in his life that people are very unaware of. He had served his time for his most recent crimes, so he was a free man. It’s interesting to note that so much of what we see in interviews over the last two or three decades, and all of the coverage on the famous crimes, we are seeing Manson through the filter of being behind bars. [On Aquarius] he is completely free. He is in the freest, most permissive society probably in history. So that took a lot of work, to get behind what we see as the notorious image of a monster and connect with a man who had been in prison most of his life, and was suddenly free and surrounded by all these kinds of people who were impressionable at [a young age] and happy to try out new things.

What kind of music did you listen to in your research?

We got sent a reading, viewing, and listening list from our show writer, John McNamara—especially the younger cast members who weren’t necessarily alive in the 60s. With Manson it was really simple. The thing was that I had to re-acquaint myself with the Beatles and really kind of listen to that because Charles Manson famously was a huge Beatles fan. That was his inspiration to become a rock star, or a pop star even. He literally [witnessed] the Beatlemania from a prison cell. I went and bought the Beatles’ albums that had been released up until that point and I bought a record player for my trailer so I could play vinyl in my trailer.

What were you surprised to learn about Manson in your research?

I think really taking myself back to that first reading of his biography about him. There is one that is called Manson in His Own Words, co-written by Nuel Emmons, and that’s him recalling his experience going through institutions—prison-like institutions from the age of six or seven throughout his teens, 20s, and into his early 30s. Just the kind of violence involved in prison-like situations when you’re a child and his relationship with his own family was just something I didn’t know. His mother allowed him to be taken away from her, effectively, and that is just something I didn’t know about him.

Also, there is an image of him when he’s about 21, and he is clean cut, in what we would describe as a suit, with a fiancé who he tried to sort of live with [and have] kind of a regular life. It’s an innocent-looking image, and that’s a tricky word to associate with him in any sense, but just that helped me connect to him before what we know of him.

Will your family in the U.K. be able to watch the show when it airs?

I understand that they will be playing it in the U.K. I’m not sure my mum is going to watch. My mum has not seen most of Game of Thrones—she isn’t quite into the whole violence on screen thing. Very sweetly, a fan of Game of Thrones edited to a DVD a full edit for my mom, which was just me without all the sexy, violent bits in it. He just handed it to me at an event; he was like, “I hear your mom doesn’t watch the show.” So I might have to do just like a cut [of Aquarius] of me singing, without all the other stuff.

Is she just waiting for you to play Mr. Darcy in Pride and Prejudice or something?

Well, she has been known to say a couple of times, “Can’t you do The Sound of Music again?” As a child, I played one of the kids [onstage in London] and I think that was her favorite thing I’ve ever done. I did do an episode of Call the Midwife a couple years ago and was so excited to say, “Mom, this is great, you’ll watch this,” and her response was something along the lines of, “Once you’ve gone through [childbirth], you don’t want to watch it on screen.” But she did watch it and she cried because I held a baby in it. She was so emotionally rocked, not by my performance, but by the fact that I literally just held a baby.