People Interview
For Stark, 34, the grounded finale made for the perfect bookend to a season that literally started with an out-of-this-world storyline.
"I think the episode, really from start to finish, is intense," he tells PEOPLE. "There is no let up ... it is grounded. We're not in space. We are firmly, in fact, literally grounded. But I love it when 9-1-1 goes really big, and then I love it when it goes really small and intense like this episode is."
He adds, "I think it does both of those things really well. And we started the season with the big spectacle, and now we're closing the season with the intense character. And I feel proud that the show is able to pull off both of those things."
By the end of the episode, Hooks was caught, Athena was embarking on a new chapter as a detective, May was starting nursing school, Eddie was back to his old self and Buck? Well, Buck made the big decision to become Theo's foster dad following the death of the little boy's parents, a situation made all the more complex since Buck was the couple's sperm donor.
Stark teased that Buck's decision will lead to some emotional moments as the show heads into its 10th season.
"Dad is a strong word," Stark laughs when asked how it feels to see his character becoming a father figure. "He's stepping up in a place that there is a void and Theo needs someone to step up and Buck is doing that. I don't think Buck is viewing it necessarily in this moment as I'm a dad now."
Fans can expect Buck's feelings to become even more complex now that caring for Theo is his responsibility.
"I think we have space to get into finding out who is or who isn't in Theo's life and why Buck needs to be the one to step up," he teases. "But yeah, I don't think Buck is yet in the mind frame of I'm this child's father now. I just think he feels like he has an obligation and a duty to be there, seeing as it's his friends that died. But I think he's certainly intimidated and aware of the magnitude of the position he's stepping into."
The actor adds that "there are going to be more difficulties" for his character as the show moves into season 10.
He explains, "I think there's going to be some emotional and possibly legal difficulties that he finds himself in. And just as we watch him navigate what the foster situation may be, and as we learn more about that foster situation, I think there'll be some difficult times for Buck ... but we like difficult times with the characters. It's interesting."
While Buck may not be ready to fully embrace the title of dad just yet, Stark is loving working with his little costars, twins Lincoln and Teddy Sykes.
"Let me tell you, I was stunned by how quickly I was like, 'I will die for you,' " he says of the twins. "They are both just so incredibly sweet and gentle little boys. For example, the scene where they were allowed to be nightmares in episode 17 and they're flinging pizza around the room, sometimes we wouldn't even make it to cut before they were trying to clean off ... Chelsea [Kane] plays Kameron, clean her clothes for her."
Stark adds, "They're just such gentle little spirits. I feel like I've been opened up already by spending time around them. And so if the story does decide that we will spend a lot more time together, I can't wait."