Just when we thought the pantry door had swung shut on the upstairs-downstairs world of Downton Abbey, Focus Features announced plans for an epic reunion: a Downton Abbey film. Capitalizing on the majesty of Highclere Castle, the movie (in theatres September 20) is the epilogue to the six-season hit ITV series-turned-PBS Masterpiece Classic, as the Queen and King of England descend upon the estate.

But it’s the chemistry between this ensemble of actors (who won two SAG Awards for Best Ensemble during the series run) that makes Downton captivating—so no surprise the cast is full of theatre greats from Dame Maggie Smith reprising her role as the Dowager Countess to Elizabeth McGovern (Time and the Conways) as Lady Grantham to Imelda Staunton in a new Downton role. Here, two other longtime theatre actors Jim Carter, who plays the stodgy yet soft-hearted butler Mr. Carson, and Kevin Doyle, who plays the bumbling if not endearing footman Mr. Molesley, reflect on shooting the movie, how their theatre training was crucial to their success on the show, and the story of how a joke audition brought Carter and Staunton together not just as castmates, but as husband an wife.

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What was the atmosphere like when you were all reunited on set?
Kevin Doyle: It was easy because we all stayed in touch. I think it's quite rare for British actors to work together, unless you're in a soap, for six years and when you marry that with the extraordinary success that the show had—and we all experienced that success together—that does something, doesn't it? It creates a sort of bond.
Jim Carter: It does create a bond. And the enthusiasm that you just expressed, about people wanting the film and getting excited about the film, bouyed us all up into thinking, "This would be great to make a film." When the series [first] finished, I thought, "Well goodbye, that was lovely, thank you very much, Downton Abbey.” But then the pressure from the media and the fans for there to be a film sort of, never waned, they just stayed enthusiastic.

Both of you have done theatre extensively. Does that training help when you're doing something as long-running as Downton?
Carter: It does. Because there are so many characters and Julian [Fellowes] writes very short scenes and a lot of the scenes are there to push on the story. You've got to develop a character that you can look after and safeguard, really. Kevin's the prime example of this. He came in as a fairly small character. He was cousin Matthew's butler who moved into the house, but because he developed that character, the writer and producers saw what he was doing and they sort of picked up the baton and developed it more.
Doyle: He was only meant to have been in a couple of episodes.
Carter: You learn how to develop a character over a long time in the theatre. Also, the discipline of theatre I think put us in good stead because Kevin, me, and Michael Fox, who plays Andy the Footman, when we were upstairs, as an actor, it wasn't the most exciting work. We were standing on duty.
Doyle: The focus was elsewhere.
Carter: But we have that discipline to maintain [presence]. The theatre background really pays dividends. And this is, you know, it's like a theatre job because you've got that company feeling. Going from youngsters—with Laura Carmichael, Lady Edith, and Sophie McShera, who played Daisy the maid, quite early in their career—through generations, through Kevin, up to me, and then to Maggie Smith coming together really as a company because there were a lot of big scenes where we just had to play together like a theatre troupe.

Carson and Molesely are such distinct characters in this series and really opposite ends of the spectrum. Who first inspired your initial characterizations of them?
Carter: For me it was very simple. I was very aware that I was standing on the shoulders of giants when I played the butler because the butler is an iconic figure British literature and film and TV: Upstairs, Downstairs Gordon Jackson playing Hudson, Anthony Hopkins in The Remains of the Day, Denholm Elliot in Trading Places, John Gielgud in Jeeves and Wooster, there are all these butlers and so I knew what the role of the butler was. And I must admit, I had to go and audition like everybody auditions and I remember feeling, “I would be very upset if somebody else got that because I've got the equipment to do this.” It needed to be someone of—
Doyle: Gravitas.
Carter: There was an early line about “Carson enters in his magnificence.” And I thought, ”I can do magnificent.”
Doyle: When you go through the green base door to serve dinner, especially if there's a king and queen, you are giving a performance.

Do you have advice for actors for how to maintain and evolve a character for an extended time?
Carter: You've got to look after your character. You've got to curate your character. Not every scene you're in will be all singing, all dancing, but you just have to hang on to the truth of what your character is doing throughout and just hope that it reads properly and comes over to an audience really. That's all you can do.
Doyle: That's a nice expression. "Curating" your character. Looking after it and hoping the writers will also look after it.

Jim, you got to be on set with your wife, Imelda. Has it been since Guys and Dolls that you two worked together, or have you worked together since?
Carter: Well, we met in Guys and Dolls 1982. We did The Wizard of Oz, she was Dorothy, I was the Cowardly Lion.
Doyle: What, were you in Guys and Dolls?
Carter: Big Jule. I was at the National Theatre doing the Oresteia which was an all-male production of it in masks. Five months of rehearsal. I saw these people coming in [to the theatre and asked], "Well what are they doing?" "They're auditioning for Guys and Dolls." "What's Guys and Dolls?" "It's a musical." "Can I be in it?" "No, you can't sing." "Oh." So, me and a couple of others were so bored in our Oresteia rehearsals we put together a joke audition for Guys and Dolls of "Brush Up Your Shakespeare" from Kiss Me, Kate, and then we got costumes and we gate crashed the auditions, not knowing what we were doing. We pulled a “gun” on the pianist and said, "Play the music." And I was the big one in the middle and we did a song and dance routine; I was the daft one who went off on the wrong foot and sang out of tune. And we danced out the door, laughing like drains and went back to our boring Greek rehearsal. Two days later, "Would you go see Richard Eyre?" I thought "Oh, shit. I'm in trouble here." And he said, "Do you want to be in Guys and Dolls?" I said, "I can't sing." He said, "Big Jule doesn't sing." And he said, "Would you mind being in drag in the Havana sequence?" I said, "Buddy, you've sold me. I'm going to do that." It changed my life. I met Imelda, got married, 36 years later, here we are.