LOS ANGELES—Dakota Johnson was less shy in our recent interview with her compared to our chat last year for “Fifty Shades of Grey.” She was her usual demure and soft-spoken self. But in “Black Mass,” she makes quite an impression despite her short role—she delivers a strong, memorable performance acting opposite veteran Johnny Depp.

Pretty in a black Saint Laurent dress, Dakota occasionally chewed her nails as we talked to her at the Shangri-La Hotel in Toronto. It was an endearing indication that the actress was not self-conscious. She turns 26 next month but she looked girlish, a look enhanced by her becoming hairdo.

To some, Dakota may be a surprising choice to play Lindsey Cyr, the longtime girlfriend and the mother of the only child of James “Whitey” Bulger (Johnny), one of the most dangerous mobsters in US history, in “Black Mass.”

But director Scott Cooper’s casting choice paid off. From a simple dinner scene to an intense argument in a hospital, both with Johnny, Dakota was a good match to the actor. These scenes are an effective counterpoint to the depiction of Bulger’s brutality, who rose to become Boston’s most notorious crime lord. He was on the Federal Bureau of Investigation’s most wanted list until his capture in 2011 in, of all places, Santa Monica, California.

The daughter of Melanie Griffith and Don Johnson will be seen next in “A Bigger Splash” and “How to Be Single” and is set to shoot “Suspiria.” And there are those two much-awaited films in her future, of course: “Fifty Shades Darker” and “Fifty Shades Freed.”

The following are excerpts from out chat.

What are your earliest memories of Johnny Depp?

I met him when I was a young girl.  We had a mutual family friend. I remember seeing “What’s Eating Gilbert Grape” and “Benny & Joon” and seeing this magical person who could just walk on screen, into a room, stand there and do nothing—and you’re fascinated. There are very few people who can command your attention that way.

And now, you are working with him.

Working with Johnny was one of the most gratifying experiences I’ve ever had. You wonder how somebody like that works and what his process is. There was a moment when we were filming the scene in the hospital.  It was a close-up shot. He was so energetically, 100 percent there.

It was as though a wave of anger, hatred and complete and utter despair from him blasted through me. I was weeping on the side of the camera and shaking. I couldn’t control myself. I was trying so hard to not bump the camera so I didn’t ruin his scene. But I was like, God, that is an artist.  That’s the magic—that’s the thing.

Is this your first time to play a mother?

I played a mother on a television show called “Ben and Kate.” I love playing a mother. I have a lot of younger siblings. I took care of them a lot. I would love to have babies.

I feel that Lindsey Cyr and Whitey or Jimmy Bulger are equals in their house. Even though he does what he does outside of the house. She’s as emotionally tough as he is. I don’t know what the thing is about powerful men that attracts women to them.What is it about a powerful man that attracts women?

Lindsey and Whitey had a relationship that was only between them. She saw a side of him that was gentle, maybe, or a bit tender. She saw the way he loved his son and that was the one thing that really got into his heart. I think that was the thing that drew her to him.

Have you been attracted to power?

Not yet (laughs). I’m working on it.

Did you get in touch with Lindsey Cyr as part of your research?

I didn’t get the opportunity to speak with Lindsey Cyr before filming or after.

There was a lot of information available about her. She has become increasingly vocal about their relationship over the past few years. I was searching for footage so I could study mannerisms or speech patterns but there wasn’t anything from that time when she was with Jimmy

Bulger. Most of the research I did was on Jimmy Bulger.

Second part of the interview after the break