Hawaii Five-0: Will McGarrett and Catherine get closure in 150th episode?

When Hawaii Five-0 hits its 150th episode, several familiar faces will return to mark the occasion.

It all starts when Steve's (Alex O'Loughlin) former flame Catherine (Michelle Borth) interrupts a hot date with Lynn (Sarah Carter) to reveal that his mother Doris McGarrett (Christine Lahti) was captured and sentenced to death while trying to free Wo Fat's father. What will Steve do? EW turned to O'Loughlin to find out:

ENTERTAINMENT WEEKLY: What does it mean to you to make it to 150 episodes?
ALEX O'LOUGHLIN:
It's kind of surreal. It's crazy. I can't believe it, on one hand. On the other hand, I feel like it's been torture, too. It's a lot of television, there's been a lot of injury, there's been a lot of water under the bridge, etc. But at the end of the day, what it really means is it's a great testament to everybody who works on the show. It's hard, man. It's hard to make a show. It's hard to make one episode, to make a pilot. It's a big deal.

What can you tease about the 150th episode and McGarrett trying to save Doris?
In the 150th, Doris comes back, Michelle Borth's character Catherine, McGarrett's long-time flame, comes back, Sarah Carter, who is McGarrett's new love interest, she's in the same scene with Catherine, so there's some pretty funny scenes. They don't know each other yet, but they're about to. There are a lot of loose ends that we need to tie up and deal with. Some of them get dealt with with closure, and one of them kind of doesn't. One of them is still left up for McGarrett. I'll let you wait to see which one that is.

How will Steve feel about reuniting with his mother?
His mother is the source of all the drive in his life. The heartache that she's caused him has been the thing that gave him what he needed to be driven enough to become a Navy SEAL, to work at that level of the military, and to do all the things at the level at which he's done them. He's constantly been trying to make up for something that wasn't there. It's a soft spot for him, and it's something that's never really going to be resolved, because she is who she is. She's in the wind, unavailable and emotionally not there. There are a lot of promises that she never keeps. It's one of those things where, as he grows up, and as he becomes a man, he has to learn to deal with it in a way that will keep him safe.

What does his dynamic look like with Catherine now? Will this episode give closure, or is it awkward to have both of his loves in the same place?
It's definitely awkward in the beginning. He's also annoyed at Catherine because of the way she left. Regardless of what was behind it, he ends up saying, "I understand, I would've done the same thing," but he deep down feels that she could've done it differently. He understands classified operations, but she did it in a pretty sh---y way. He's been really patient with that woman, too. He kept waiting for her and being patient. Still, he was going to propose, but she blew it in the end. He's not resentful, but he's trying to move on, and here she is again. They get to a really good place. They get to say the things that need to be said, and hear each other say those things. I really like the place that they get to. I hate the word empowering, but they both end up in better shape as a result of it.

How do you think this episode honors the show?
It's classic Five-0 espionage, wild action. We bring the unrealistic into reality. There's teamwork. Pardon the pun, but there's a MacGyver-y aspect to it. There's a lot of black ops aspects to it. There's a lot of knife work and a lot of explosions, airplanes, gunfire. It's Five-0 at its best as far as the action goes. Plus: There's a whole bunch of character threads through the story that are getting dealt with. It's good. I think it's going to be satisfying for the fans.

Hawaii Five-0's landmark episode airs Friday at 9 p.m. ET on CBS.