Broadway vet Kristen Beth Williams has been a constant fixture on Broadway since she made her Broadway debut in Promises, Promises in 2010. In her first three Broadway shows, she understudied three different Tony-winning actresses: Katie Finneran in Promises, Promises; Sutton Foster in Anything Goes; and Judy Kaye in Nice Work If You Can Get It.

For the last year, Williams has been touring the country with A Gentleman’s Guide to Love and Murder, 2014’s Tony-winning Best Musical, which finally comes to Boston Oct 18.

You have been a pretty consistent presence on Broadway for the last five years, and I think it’s so interesting that in your first three shows you understudied the person who won the Tony.

Yes, actually! In my first three Broadway shows I’ve covered Tony Award winners in every single one of them.

It must be a strange feeling to think, as an understudy, that the people in the audience might be looking forward to seeing the person who just won the Tony, and then they get a slip of paper in their playbill with your name on it.

I’m sure it is, you know. Luckily for me, with Promises, Promises, I only had one shot and I sort of knew that. I went on for Katie Finneran the day she got married, actually. We kind of knew that was going to happen, so I had quite a bit of time to prepare for it. And what I remember most leading up to that was Katie pulled me aside one night and said: “You know what, you can’t go too far.” She basically told me to go big or go home. You’ve got one chance to do it, so just go out there and do it and don’t apologize for it. That has stuck with me my whole career of understudying Tony Award winners. The hardest one that I covered was Sutton [Foster], actually, because she had won the Tony and the show was built around her and everything that she could do, and she is such a dynamite performer; and she’s such a darling and so beloved in the Broadway community that stepping into her shoes was, I think, a little more intimidating than anybody else’s. Again, perfect storm—I was the second cover, I was never going to go on; and then the week that her first cover took a vacation, Sutton got violently, violently ill, and I did almost six full shows.

That must be so thrilling; Reno is one of those dream roles.

It was, it really was. As a little girl growing up from Mesquite, Texas, I always considered Broadway to be the dream, never the goal—I tried to keep my goals very realistic in that I would like to work professionally as an actor and not have a side job—that’s the goal. Broadway is the dream: if [I] get there, great. Once I got there, I thought, okay, now I need a new dream. And you don’t realize that your dream is to take a final bow on a Broadway stage until you’re actually standing there doing it. And I called my mom on my walk to the subway that night and said, “Mom, I took the last bow on a Broadway stage tonight, and if that never happens again for me, I can at least say that I did it.” And that’s really astounding.

What are you looking forward to about being in Boston?

I worked about 10 years ago at North Shore and at Reagle Music Theatre so I kind of know the area, but I know it from 10 years ago, so I’m really excited to come in and walk through all of the history of downtown Boston. There are several big history buffs on this tour, and we love to just go to the museums and walk the trails and see all of the things that we can see. There are a couple of battlefields that I would like to get to that I haven’t ever seen, and we’re doing a charity ride at SoulCycle in Back Bay on Friday the 21st at 2 pm for Broadway Cares/Equity Fights AIDS, so we’re very excited about that.

You had said that this role fits you like a beautifully tailored suit. Why is that?

Oh gosh, it makes me sound like a horrible person if you know the show. [laughs] She’s so wonderfully self-centered and devious in a really fun, fantastic way. And I don’t know what that says about me as a person. I just have a ball playing her. It’s a superbly well-written character with a lot of layers, so she’s really fun to play.

A GENTLEMAN’S GUIDE TO LOVE AND MURDER. 10.18-10.23. SHUBERT THEATRE, 265 TREMONT ST., BOSTON. AGENTLEMANSGUIDEBROADWAY.COM