[Warning: The following article contains major spoilers about Friday's episode of Hawaii Five-0. Read at your own risk!]

Hawaii Five-0's 150th episode may not have given McGarrett-Catherine fans the romantic reunion they had hoped for, but it provided McGarrett (Alex O'Loughlin) with some much-needed closure about the way their relationship ended.

"It's now been finished the right way," O'Loughlin tells TVGuide.com.

Catherine (Michelle Borth) comes back into town to tell McGarrett that his mother Doris (Christine Lahti) was caught trying to break Wo Fat's father out of a CIA black ops site in Morocco. The two embark on a rescue mission together, leaving McGarrett's girlfriend Lynn (Sarah Carter) to enjoy a romantic dinner for one. Awkward!

Once the action-adventure part of the episode is out of the way and Doris is safe and sound, Catherine (who, earlier, learned from an unwitting Lynn that McGarrett was on the verge of popping the question when she disappeared) tells McGarrett that, although she would have said yes to his proposal, she wants to put her career first for now and she's happy that he's moved on with Lynn. And then she's off again.

TVGuide.com chatted with O'Loughlin about where McGarrett and Doris are going from here, whether the serial killer storyline will come back into play, and why McGarrett would be an "idiot" to get back together with Catherine.

Hawaii Five-0's 150th episode gives "closure" to McGarrett

TVGuide.com: After this episode, will we see McGarrett and Doris have more of a relationship going forward?
O'Loughlin:
I don't know about that. Doris, she pays lip service to a lot of things. She was a really good mother when he was a kid, and then she disappeared. She's so used to the nomadic life - and by the way, she's still got a lot of stuff to work out with the government. She ain't exactly in the clear. She's got a lot of explaining to do and she's got a lot of sort of ducking and weaving ahead of her in her own story. There's talk of, "I'll move down the street. You'll see me every day." He's like, "Jesus Christ, Mom, would you stop with that sh--?" Because he knows it's never gonna happen. She's not that person. She can't settle down, and it'd be dangerous for her to settle down. Because there's probably a lot of people in the world who want to kill her for her secrets. So I think that part of McGarrett in this episode finally has become resigned to that, and he's able to protect himself a little bit more emotionally from what that might look like one day. I think he really believes he's going to bury her. She's not going to bury him.

Do you know whether there are plans to bring her back for more episodes this season?
O'Loughlin:
I do not.

Do we get to see any more of what McGarrett finds in the box from Doris?
O'Loughlin:
Not to my knowledge. To me, the way that read and played was that it was like Doris said, "Look, I left a diary there of my deepest personal secrets and I want you to read it. I want you to know who I was. I want you to know who I am. I want you to know the things I haven't been able to tell you, the things you might not know. I want you to have those. I want you to have that piece of my heart." So, it felt like a really beautiful movement in the correct direction for this relationship between mother and son. It felt like a great thing of trust from her, and it felt like an olive branch. Like her just saying, "Look, when I say I want to give you transparency, I really mean it. Here's me showing you that." So I think that [scene is] a lot more about their relationship and what happened in the relationship between these two than any government secrets or anything.

Switching gears to Catherine, she gives McGarrett her blessing about his relationship with Lynn. Based on that final scene between Catherine and McGarrett, is there any hope for them to reunite?
O'Loughlin:
I have no say in what they write, but if you're asking me what I think, McGarrett doesn't need Catherine's blessing to do anything. The way she left things, it was pretty disgraceful. He is a high-end special operator for the US government. He was at the highest level. And so, you don't need to pull the top-secret card with someone like that, who understands the lay of the land. There's another way you can do it that's not gonna hurt people. So, the way she did it was kind of gnarly. It was much more like Doris. And so, as far as he's concerned, he's going to do what he's going to do. He certainly doesn't feel obliged to make sure he's got a blessing from her.

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That being said, it does offer some closure for him. It's now been finished the right way. I just think if she came back and went, "I'm available"... first of all, he really likes Lynn. She's a great girl. And I don't think he would just ditch her. That would be the wrong thing to do. And if he just jumped back into a relationship with Catherine, I think he's an idiot. You have no self-respect? There's no sense of self-protection or self-preservation? If that happens, I'll play it the way it needs to be played, but it would seem like doing something like that would be a cry for help. He's an idiot if he does. That would have to be a means to an end for a storyline.

Will the serial killer storyline from earlier this season come back into play? We know Madison Gray is still out there.
O'Loughlin:
I don't know. In true Five-0 style, we've just left a gigantic storyline on the shelf, which may or may not be picked up later. But there's a serial killer on the loose. I can't give away too much, but there's other things that they just sort of leave hanging there. I'm like, "Jesus, and then we all just go for drinks at the Hilton afterwards?" But yeah, I don't know. Wasn't Claire Forlani great?

Yes, that was my next question — will we get to see any more of Alicia Brown this season?
O'Loughlin:
I hope so. She's the best. We had a blast. We just laughed the whole time.

Hawaii Five-0 airs Fridays at 9/8c on CBS.

(Full disclosure: TVGuide.com is owned by CBS.