When DECIDER first talked to Oliver Stark ahead of 9-1-1 Season 9’s premiere, he knew that his character Buck would continue “a journey of becoming and finding himself.” But he had no idea that by the end of the 18-episode run he’d be finding himself with and through someone new: his biological son, Theo.

Back in Season 6, Buck agreed to be a sperm donor for his pal Connor (Colin McCalla) and his wife Kameron (Chelsea Kane), but even after he eventually delivered their baby on his own couch, held him in his hands, and called him “perfect,” Buck — and Stark — never imagined the storyline would reappear in the future, especially not in such a deeply dark, life-altering way. The 9-1-1 star even admitted that the Season 9 twist was such a shock that it took some convincing to get him on board.

“Tim Minear, who writes our show, called me when we were shooting Episode 15, and said, ‘I’ve got something for you to move Buck forward.’ And I like, ‘OK, great!’ thinking, ‘Is it going to be a love interest, or what?’ And he goes, ‘Sperm baby,'” Stark told DECIDER as he flashed a contagious grin from the burnt orange couch in our Midtown Manhattan studio. “It’s been a few seasons since that storyline first came around. So it didn’t immediately ring a bell what he was talking about. I said, ‘Say more.’ And he said, ‘I’m going to bring back the sperm baby.’ I said, ‘OK, cool. I love having Colin and Chelsea, who play Connor and Kameron, on the show!’ And he said, ‘I’m going to kill them.'”

When chatting about Season 9’s finale, Stark admitted he was “a little apprehensive at first” of the bold move designed to end the season with Buck fostering Theo. “I was like, ‘Oh, wow. That’s a huge thing to bring into his life.'” What ultimately changed his mind was working with twins Lincoln and Theodore Sykes, who play the four-year-old. “They really won me over. And I understand Tim’s vision for it now, and I’m happy with the way it’s ended up playing out… [The writers have] not steered me wrong thus far, and I have always had a lot of trust in them.”

As fans saw through Hen (Aisha Hinds) and Karen’s (Tracie Thoms) foster parent journey earlier in the series, Stark believes that Buck will encounter a trying time in Season 10 as he navigates the foster system and the show explores why he’s the one caring for Theo. Though Stark sees a look at the process “dominating the storyline,” it’s certainly not the only aspect of this new relationship he wants or expects the series to dive into.

In Season 9’s penultimate episode, Buck and Theo’s unconventional meeting offered an initial sense of the child’s kind heart, as well as his familiar impulsivity. When Buck had the family of three over his house later, however, Connor and Kameron compared Theo to a “heat-seeking missile” and revealed just how full of energy and unpredictable he was. “He needs to live as much as possible as fast as possible,” Kameron explained, essentially describing Buck back in the day. The couple wondered, “Is this just his personality, or a diagnosis?” And that question is one Stark would be open to trying to answer more explicitly down the line.

For years, 9-1-1 viewers with ADHD have seen themselves in Buck, and the actor also has acknowledged that representation. While Stark hadn’t thought too much about Buck seeking an official diagnosis, when asked about the possibility in wake of that recent conversation, he said, “That’s really interesting… If Buck ends up learning a little bit about himself through Theo, I think there’s absolutely something there.”

“I’ve always loved this idea that maybe Buck does have ADHD and that that’s one of his superpowers in terms of being a great first responder. So if he can actually learn that about himself within the show, I would love to see that,” Stark continued. Though a running joke throughout DECIDER’s conversation with the 9-1-1 star was that Minear doesn’t read his interviews for show inspiration, I know for a fact the showrunner/writer will consider this specific storyline, because I also asked about it during my Season 9 finale interview with him. (Stay tuned for that full conversation next week!)

“I’ve always loved this idea that maybe Buck does have ADHD and that that’s one of his superpowers in terms of being a great first responder. So if he can actually learn that about himself within the show, I would love to see that.”

Oliver Stark, 9-1-1

Theo may have been “a little monster” at Buck’s house as he ripped flowers, sprayed chocolate milk, nearly burned the place down, but Stark took a moment to stress how different the young actors are from their character. “The twins are so sweet, like so sweet. In the scene where we’re having dinner and they’re throwing pizza at the parents, sometimes before they even called cut [one of them] would run over and want to start cleaning it off, saying, ‘I’m sorry, I’m sorry!’ But it’s funny, as soon as you give them license to misbehave you see their eyes light up like, ‘Wait, I get to destroy this?! And it’s like, ‘OK, yeah. There’s a monster inside everyone,” he added with a chuckle.

Shortly after Buck hosted Theo and his parents, he and the 118 responded to a pile-up on a bridge that involved a boat and several cars. Upon realizing Connor and Kameron were unconscious in one of the vehicles, Eddie tried to protect Buck from witnessing the heartbreaking scene, which served as an intentional callback to the Season 2 scene where Buck tried to prevent Eddie from seeing his late ex Shannon’s (Devin Kelley) crash.

When asked about poignant parallels between Buck and Eddie’s lives — which include the fact that Eddie was also absent from his son Christopher’s (Gavin McHugh) life early on — Stark said they foreshadow what a crucial role the single father will play in Buck and Theo’s life come Season 10.

“Through those parallels, Buck is going to be going through steps and difficulties that Eddie himself navigated. Those are tie-ins to the fact that he’s going to have to be a prominent part of this story and is going to be there for Buck. And Buck is going to — more than anyone, I would assume — lean on him… And because Chris will be almost big brotherly to him, he can do some babysitting.”

“Those are tie-ins to the fact that [Eddie’s] going to have to be a prominent part of this story and is going to be there for Buck. And Buck is going to — more than anyone, I would assume — lean on him.”

Oliver Stark, 9-1-1

Over the years we’ve seen Buck help care for Christopher, serve as a mentor to younger characters like Harry (Elijah M. Cooper), and learn invaluable lessons from his late father figure Bobby (Peter Krause), so he isn’t completely inexperienced in this department. Stark also thinks that through Buck’s rocky relationship with his own parents, he learned the kind of caregiver he doesn’t want to be.

“I think their love was always restricted, and it obviously drove back to certain personality traits that aren’t always in his best interests. And I think Buck would never want to, as we sometimes do, pass on the bad traits that we receive down. I think he would want to break that cycle. And not put such constraints on the way that he loves,” Stark explained. 

When asked to tease how this crucial storyline will evolve in Season 10, the 9-1-1 star said, “It will be interesting to see what the work/life balance is for Buck. Whenever you have kids around you, it’s such a mirror. You learn so much about yourself. And honestly, in these last couple of episodes, even I did about myself through working with the kids. So I think Buck figuring out a lot about the person who he is through somebody else and through this mirror of a child is going to be very prominent.”

Stay tuned for Part 2 of our conversation with Oliver Stark, plus an interview with Tim Minear about Season 9’s finale and what’s to come.

9-1-1 Season 9 is now streaming on Hulu.