A scout troop out camping in Pennsylvania is terrorized by a bizarre electrostatic phenomenon that yanks the battery out of their car and leaves their leader dead but hovering in midair. Oddly, S.H.I.E.L.D. sends in Coulson's team rather than calling up Thor and asking him, "Sooo…what'cha been doin'?" While they're investigating -- which entails Simmons getting zapped by the body like a metal doorknob in a carpeted room, May questioning the assistant scoutmaster, Fitz pouting even more than usual, Skye doing the cyber-legwork on the victim, and Ward still grumping at Skye -- another victim is taken out in a similar manner. Skye quickly finds out that both men were firefighters based out of the same station house, and were both at the Battle of New York. Coulson, Ward, and May head to the firehouse to find out who or what might be targeting these particular firefighters, and Coulson gets to watch as a third man starts showing signs of becoming a human lightning bolt. They soon figure out that the firefighters aren't being murdered after all -- they've just had the spectacular bad luck to have contracted a virus from a Chitauri helmet that the ladder company kept as a souvenir. There's no way and no time to save the third firefighter, but at least Coulson is able to sit down with him in his last moments and share the reassuring story of his own death -- or at least the version Coulson thinks he remembers.
In the aftermath, the remaining firefighters are quarantined and the team takes possession of the helmet so they can bring it to a research facility somewhere in West Africa. While en route, Simmons excitedly realizes that the virus is transmitted not by any previously known terrestrial method, but through electrostatic shock. And since she got a jolt from the first victim, she now has it herself. Which is a buzzkill that will ironically end in a very loud, killing buzz.
Coulson isolates Simmons in the lab, not that that's going to help the rest of the team when she turns into a walking Tesla coil inside a plane that's over the middle of the Atlantic. In essence, she has two hours to find her own damn cure, and it is not going at all well. Thus Coulson gets an order to jettison any "infected cargo," a directive he obviously ignores. Ward opens up to Skye about the helpless feeling of facing an enemy he can't beat up, and Fitz wastes a few of Simmons' last minutes arguing with her about how they shouldn't be in the field in the first place. But then that eventually leads to them coming up with a solution that includes harvesting alien antibodies from the Chitauri helmet. Fitz heroically joins her in the lab to work side by side while the others watch. It looks like they're going to pull it out, but when the third try apparently fails as well, Simmons takes it upon herself to exit through the rear. Of the plane, that is. And this just moments after Fitz realizes that the cure works after all. Fortunately, Ward grabs a parachute and dives after her, administering the vaccine -- sorry, anti-serum --in midair. So that turns out okay, though Coulson gives them some tough love about it afterward.
Through all this, Coulson and May have been dancing around the subject of some ahead-of-schedule medical tests he's been undergoing. He's been playing it off like it's the doctors' idea, and they show nothing abnormal, but in the end he confesses to May that he ordered them himself because of how different he feels since, you know, dying. May assures him -- from what seems like personal experience of her own -- that experiences like his change anyone who goes through them, and she gets us a good look at Coulson's scar in the process. Coulson not only buys it, he also faces some of the blowback from his earlier insubordination with another possible byproduct of his fatal run-in with Loki: a pair of great big adamantium balls.