9-1-1 puts the spotlight on the best team within the 118: Hen (Aisha Hinds) and Chimney (Kenneth Choi) in the latest episode. She brings her suspicions about his temporary replacement, Jonah (Brad Durfee), to him, and they investigate to see if he may be responsible for killing, rather than saving, the people on calls.

“Hero Complex” opens with a look at how it all began: Jonah was sort of the weird kid, until at the age of 13, he saved his bus driver. Then, he became a hometown hero and was introduced to the “rush” of saving lives and the attention it brought.

Following the funeral of a dispatcher who should have survived, Hen admits to Chimney that it reminded her of a previous call: a man had been bit by multiple spiders and was stable when she left him alone with Jonah. Then, he coded, just like the dispatcher. Chimney believes her (“always,” he says), and they begin their investigation by sneaking into Bobby’s (Peter Krause) office to look at Jonah’s paperwork on the two patients. Chimney, meanwhile, goes into their captain’s computer (password: NashBby_118 — oh, Bobby) to access Jonah’s personnel file. There is a pattern in Jonah’s reports and history: He moves around a lot. They very badly cover when fellow firefighters Lucy (Arielle Kebbel) and Ravi (Anirudh Pisharody) question their presence at the 118 on their day off.

As they learn from a paramedic, there’s a third victim who fits the pattern, and he died after seemingly being fine before Jonah was left with him. The only problem is they don’t have proof, and it’s not like the LAFD would’ve hired him if he had a trail of suspicious deaths in his other cities. But, as Hen’s wife Karen (Tracie Thoms) points out, there could be suspicious behavior because no one starts with murder.

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That’s when Hen uncovers Jonah’s “origin story,” and they realize that he doesn’t want to kill people, just push them to the brink of death to have the glory of saving them. And so they go to Buck (Oliver Stark) and Taylor’s (Megan West) to watch the latter’s footage of the call center fire, while making sure it’s all “off the record” with the reporter. She agrees. (But later, Buck finds her digging into it. That can’t be good for their relationship.) They see that the dispatcher is fine, but then. Jonah gives her something, which is against protocol based on her symptoms. It looks like he gave her some sort of drug to stop her heart.

Hen and Chimney then bring their suspicions to Bobby and Athena (Angela Bassett). He calls the chief, who opens an investigation into the dispatcher’s death. For now, Jonah’s being put on light duty, pending the results. And it turns out Athena’s right to warn Hen to be careful as she’s leaving. The sergeant doesn’t think that Jonah will take kindly to being exposed if they’re right — and he then calls Hen as she’s driving home. Did she file a complaint against him, he wants to know. (Has “Henrietta” ever sounded more like a threat?)

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As Jonah sees it, she never gave him a chance to prove himself, so that’s what he’s going to do. Hen assumes her family’s in danger and quickly calls Karen to get everyone out of their house, but her wife realizes that she’s not the one Jonah is jealous of: Chimney is. By the time Hen gets to her best friend’s place, it’s too late. Jonah comes up behind her, injects her with something, and she wakes to see he’s holding her and Chimney — hooked up to a heart monitor — somewhere.

Jonah thinks that Hen’s past heroics saving lives puts them on the same team, and to prove that he’s doing the same as she did, he stops Chimney’s heart then brings him back with a defibrillator, right before her eyes. The rush of watching someone walk up to deaths’ door, then bringing them back is like being God, Jonah says.

Meanwhile, Maddie (Jennifer Love Hewitt) stops by Chimney’s to drop off their daughter and finds his phone ringing on the floor. It’s Karen calling, and the two begin putting the pieces together.

Jack Zeman/ FOX

Hen pleads with Jonah to let Chimney go, and he agrees … by stopping his heart again, then bringing him back. But this time, it takes a bit longer. It’s utterly heartbreaking watching Hen be forced to watch her best friend die, knowing that his life is in Jonah’s hands. When Chimney begins to stir and work on freeing his hand, Hen keeps Jonah distracted, calling him sloppy, then telling him the other man’s not breathing. When Jonah checks, Chimney uses the defibrillator on him. With Jonah unconscious, the two are safe. It was a team effort, Chimney says.

Bobby and Athena arrive on scene as the police are leading Jonah out of the house in cuffs, and 118’s captain immediately punches him. “I trusted you,” Bobby says before punching him again. After he sees Hen and Chimney are alive, he apologizes to them. This is, of course, all over the news, surprisingly fast for Buck’s liking, and as Taylor delivers her report, he leaves her a voicemail asking what she did.

Hen and Chimney are both going to be fine, though they do need to stay overnight at the hospital for observation. Karen rushes over to them in the ER, admitting she had been preparing herself for the worst case scenario. But she played a role, too. After all, she’s why the police arrived on scene so quickly.

The next day, Hen checks in on Chimney to see if he’s ready to break out of the hospital with her. “I’m all in, ride or die,” he says, and that has new meaning now, doesn’t it? Considering Chimney did almost die, Hen regrets getting him involved. “Come on now, that’s not how we do it,” he reminds her. “You jump, I jump, or something like that. You think I was going to let you go after that creep by yourself?” She knew he’d have her back.

“Everyone thought I was crazy, that I was being too hard on him because he wasn’t you but you never flinched. You were on board from the start, ready to go to battle with me, even when I had no proof, no idea if I was even right,” Hen says. “You’re always right,” Chimney tells her, pointing out, “That’s kind of our shtick. You’re the genius, I’m the comic relief.” But. “you’re so much more than that. You’re the best friend I’ve ever had, Chimney, and I can’t imagine my life without you,” she says, and he promises, “you’re never gonna have to.” That has to be one of the best scenes of the season.

9-1-1, Mondays, 8/7c, Fox