The most striking thing about actor Alex O’Loughlin, as he drops into a plush chair on the set of "Hawaii Five-0," is the serenity on his face. He is healthy and happy. A whole man.

O’Loughlin, the star of "Five-0," has been hard at work since July on the third season of the popular CBS television drama, which debuts tonight with a special Sunset on the Beach screening in Waikiki and Monday for the rest of the country. But the real work took place long before the cameras started rolling on the new season.

In March an aura of calm seemed a distant, unlikely prospect after O’Loughlin required a hiatus from the show so he could receive help getting off the prescription pain medication prescribed for a nagging shoulder injury.

The actor says that leaving, even briefly, was difficult because he loves "Five-0" and is lucky to be a part of it.

The experience changed the 36-year-old Australian, who delighted fans in August with news that he and his girlfriend, model/surfer Malia Jones, are expecting a baby. It’s the second child for both, who have offspring from previous relationships.

O’Loughlin’s smile is broad and his laughter a rolling acknowledgement when he notes his "new status."

"It’s a wonderful stage," he says. "I’m having the best time of my life."

That much is obvious.

During a conversation in the make-believe office of his character, Navy SEAL-turned-lawman Steve McGarrett, the actor talked about new plot twists in the show, an "epiphany" regarding his role as a key member of the "Five-0" cast, and the joys of raising a family in Hawaii.

QUESTION: How much input do you have when it comes to the story arc of "Five-0"?

ANSWER: I’m less involved in the creative side of things as far as story line and stuff like that. I pitch things to (executive producer) Peter (Lenkov) for week-to-week stuff … but really I kind of leave it up to those guys. If something that I am passionate about comes up, I give it to them, but I am certainly not going to take credit for any sort of big story points. From week to week I get the scripts, and I am as surprised as you guys are when you see the show.

It’s terrific when the new script comes out. I am always eager to read it and see what’s happening and see what sort of new information is going to come up and what I am going to get to play with.

Q: That story line left everyone surprised at the end of the Season 2 finale.

A: Yeah. His mother has shown up again, and for the last 20 years he’s thought she was dead. Not only that, but essentially the brutal killing of his father was directly related to his mother faking her own death, because his father was in active pursuit after all those years, constantly, for her killers. The whole family has been looking for answers. …

It’s just a whole nother level of confusion and mistrust and questions. And also regret and resentment toward his mom. I think he definitely has mixed feelings toward her.

Q: Well, he was certainly surprised in the final moments of Season 2.

A: Absolutely. And how do you process that information? Of course in the first episode we explain what happened to her and why she did what she did. And of course it was well-intentioned, but it’s still family.

Family is such a tricky thing for all of us. I don’t know one person who doesn’t have some sort of something with their parents or siblings or something. You can chose your friends but you can’t chose your family … and as the story progresses, what becomes really clear quite quickly is Steve’s mistrust of his mother, and that’s a really difficult place to be, to not trust the one you should trust more than anyone.

Q: When "Hawaii Five-0" first started shooting episodes in 2010, you said it was a stunt-filled, physical show that made a lot of demands on your body. In Season 2, that took a toll on your shoulder and prompted a brief hiatus for you. Are you approaching the demands of your role any differently this season in order to remain healthy?

A: Everyone knows how rough it got for me. Look, that stuff happens to professional athletes all the time. I’m not claiming to be a professional athlete, but I am very athletic and I do a lot of physical stuff, a lot of stunts. I came back into Season 3, and I realized that … I am having a baby and I have my 15-year-old at home as well who lives with me and I have a lot of responsibilities. But more than that, I have a responsibility to myself, and that’s something that I think I neglected a little bit. Not in a careless way, but this is the first show that I have had that has succeeded. I think I felt like it was really on my shoulders, and I had some sort of Superman complex — I’m going to be all right; you can’t hurt me. But you can. I’m just like everyone else. Bang me around enough, eventually something’s going to break.

It’s actually really peaceful in my life now with this epiphany that I’ve had. And I still get into it and do some action stuff. I love all that stuff, but I don’t take the risks I was taking before. And it is not just so I don’t get hurt; it’s honestly because I don’t want to.

Q: How important is your fitness routine to your health?

A: I do all sorts of training. … I bike. I run. But I go through phases where I use weights more. Lately, for the last six months, my primary focus has been jiujitsu. It seems to be a terrific sort of all-arounder for me. I do other bits and pieces here and there, but I do that about two or three times a week. It’s great for tendon strength, which is one of my big problems: the tendinitis in the shoulder and stuff like that.

But it’s like you were saying: I’m not 25, I’m 36, but I’m going to be 50, God willing, at some stage, and I want to still be in the game. I want to be active with my kids. I’m an active guy. I can’t just sit around. (Exercise is) a real important part of the balance in my life. I don’t want to get to a stage at a young age — and I consider 50 a young age — where I can’t do what I want to do. I’m playing it smart.

Q: At a panel discussion in February 2011, you told the audience that Hawaii had become your home, that your heart was here now and that you wanted to raise your family in the islands. It would seem to be as good as it gets right now.

A: Family is my first priority. I hate to tell the producers of this show that, but that’s my first priority. … The show is my second priority. The show is extremely important, and you see how much I put into the show, so you can only imagine how much I put into my family. Every spare minute I get, I am at home. I’m with the kids, I am with Malia.

I’ve lived a lot of life, I think, for my age, and I’ve done a lot of the stuff that I’ve wanted to do, and there is plenty more for me that I am going to do. But at this stage the contentment that I get from just hanging out with the kids and at home, and my house is so beautiful. I bought this fixer-upper that was built in ’52 and things are forever falling apart and not working. I forever have little things to do. I work on it myself and get help working on it as well. I can do some things. That’s the stuff that I really get off on. I love it more than anything.

So I don’t feel like I am missing out on not going to clubs. That stuff went away for me a long time ago. But sometimes, like any parent will tell you, you can get fed up, and I wish, ‘Geez, I just wish I had a second to myself to just be selfish.’ But the great thing about parenting is you don’t have to think about yourself anymore because you are so busy thinking about some small people.

Q: Children grow up too fast, though, and then you have an empty nest.

A: I think I have a really fantastic balance being the lead of a big show and being a family man. I balance it really, really well. But is there more that I would like to do on the family side? Of course there is. But it’s funny about what you’re saying. Sometimes I look around the house and say, ‘Geez, who has drawn on the wall? Why can’t you guys put your toys away? What is happening here? Who spilled something on the couch and didn’t tell anyone?’ But then I picture myself in 20 years’ time and the kids are all gone and there are no toys and it’s quiet and I’m like, I don’t know, man, that’s what gets me through the mania of those moments.

Q: Is it true you pushed hard over the summer for a third Sunset on the Beach premiere?

A: Yes, it’s true. I don’t want to take credit for Sunset on the Beach, and I don’t know if anyone was listening to me pushing. But when I heard they were not sure, I was disconcerted but also concerned and a little annoyed. And they may have been planning to do it all along. I’m sure they probably were. But it is so important, man. It’s so important for the people of Hawaii. It is not about me walking down a red carpet and cameras. It’s about people who want to come and rejoice in a show that has come back and is doing really well for the islands.

It’s about the people; it’s not about us. That’s why I pushed for that.