Captain Hook (Colin O’Donoghue) has had a tumultuous journey on “Once Upon a Time,” evolving from villainous pirate to somewhat reformed pirate with aspirations of heroism. His hard-earned goodness will be put to the test in the March 22 episode, “Poor Unfortunate Soul,” which explores Hook’s “complicated” history with Ursula (Merrin Dungey).

Variety spoke to O’Donoghue ahead of Sunday’s episode to learn more about Hook’s past with the sea witch, his suspicions about Mr. Gold/Rumplestiltskin (Robert Carlyle) and his deepening relationship with Emma (Jennifer Morrison). Light spoilers ahead.

In the present day, we know that Hook’s is investigating Rumplestiltskin’s plans by quizzing Ursula for information — what’s their dynamic like?

Hook has a complicated history with Ursula, and when they first saw each other a few episodes ago in Storybrooke, it was kind of an icy “Captain” from Ursula. So we learn exactly what happened in the past between them. Hook befriends the young Ursula [Tiffany Boone], and he agrees to help her because her father, Poseidon [Ernie Hudson], uses her voice to ruin pirate ships and run them into rocks, and she doesn’t want to do that. They do genuinely have a mutual respect for each other at the start in the past, and then we learn what exactly went on.

Given that icy reunion, it’s obvious that his attempt to help her didn’t quite go according to plan — what can you preview about his motivations during their flashback encounter?

He’s out for himself but… even in that “badass Hook” phase, he had a code. Hook always tried to live by this crazy code that he had, even though sometimes it meant he would step on people. But Ursula does something to help him and he’s willing, then, to help her run away. Then he does something… else. [Laughs.]

Does he feel any remorse for how things transpired between them in the past?

You see that in present day, Hook decides to take a leaf out of Emma’s book and he offers her a chance at her happy ending in exchange for finding out what Gold is really after, and so Hook at the minute is trying to be the best man that he can be, because he genuinely loves Emma and he wants to make a real go at it. Sometimes he makes mistakes, but everybody does.

[Showrunners] Adam Horowitz and Eddy Kitsis recently told reporters that Hook has some things going on in his head that he’s concerned about — can you elaborate on that at all?

You can see even in last week’s episode and the week before, he’s still struggling with trying to shake off the darkness he’s allowed in over those hundreds of years. And that’s a very difficult thing for him to do; psychologically, it’s very difficult for him to all of a sudden try to become a hero. He’s always going to fall through the cracks here and there, and as much as he doesn’t want to, sometimes the old pirate just comes back.

Right now Emma’s parents are keeping a massive secret from her, just as she’s starting to open up her heart again — will Hook be her rock when everything hits the fan?

Hook is a rock for Emma. he tries to help her navigate her way through the emotions she’s feeling and in some ways draw on his past to try and help guide her. But you’ll find out later in the season how exactly that goes… But he’s definitely there for her and trying to help guide her in the best way that he can.

We’ve seen hints that Emma could channel her own dark side and align with the Queens of Darkness; if she did go bad, do you think Hook would want to embrace his villainous side along with her, or do you think he’d want to try and keep her on the side of good?

That’s a difficult question, because we have seen, since he’s tried to become a hero, he has slipped here and there and done some things… out of what he felt was trying to do the right thing, he’s done a couple of bad things. He’s still a pirate, he’s still Captain Hook, so maybe he could embrace a little bit of his darkness again. I don’t know, I guess we’ll have to wait and see…

In the midseason return, Hook told Belle that love is a weapon — does that apply to his relationship with Emma now that he’s finally allowing himself to be vulnerable and love someone again?

I’m not sure if that’s the case with Emma; I think he’s given over all of himself to Emma. At the start, he was scared to allow that love in because of what had happened with Milah and how that sent him on a hundreds of years [long] journey of hate. But I think now that he’s allowed himself and admitted to himself that he’s in love with Emma and that he’s willing to do that again… Hook commits whole-heartedly to something. When he’s decided that’s it, he’s 100 percent committed, so that’s where he is with regards to being in love with Emma.

He’s clearly still suspicious of Rumpelstiltskin’s motives in Storybrooke and the two have a very long history, so what’s coming up for the two of them?

Hook spent so long trying to find a way to kill Rumpelstiltskin, they just plain don’t like each other. At the moment, because Hook is trying to be a better person, he’s trying not to give in to that hatred again. But he still can’t stand Rumpelstiltskin so you see some of that come into play. And Rumpelstiltskin pretended to be Hook in the last episode, so he can’t get away with that. [Laughs.]

“Once Upon a Time” airs Sundays at 8 p.m. on ABC.