The horribly decorated Serenity floats toward Reaver space. Mal won't talk to anybody, goes to hide in a room off the kitchen. (There's a deleted scene here, again for good reason, where he finds Inara there, going through the previously-mentioned truck of "stuff," and they have a brief discussion about Simon handing out overdoses of morphine -- of course, we know Inara keeps one of those anyway, but she's too classy to mention it -- among other things, and ends with Mal's plaintive question, "Why didn't you leave?" and her similarly painful response, "Why didn't you ask me not to?" He, of course, takes off immediately, because even a crisis like this won't force him to tell her the truth.) The whole crew waits in the cockpit with their breath held, as Wash guides her through the wreckage and chaos of the Reaver ships. Scary howling and static play across the radio; River is rapt. Wrongly-engineered ships split apart, entropy is everywhere, debris is scattered across everything. The tiny little Firefly slowly makes her way though the mess. A collective sigh of relief is heaved as they clear Reaver space and reach Miranda.
The Operative, exasperated, on the bridge of his ship: "Define 'disappeared.'"
They enter Miranda space and land, detecting no abnormal readings, tectonic instability, radiation. Down on the planet, in their EVA suits, they freak out about how perfectly habitable the planet is -- cities, land masses, all blank and livable and empty. It's a ghost town, in perfect and clean brightness. They finally find a body, with no visible signs of damage. Mal wonders if it's poison. Jayne sees another one, lying limply in an undamaged shuttle. It's as scary as a horror movie, but the light is so bright. The crew slowly eliminates all possible reasons for their death: gas, poison. There's no explanation. "They didn't fall. None of them. They just lay down." River gets more and more terrified, the camera whirling around her as Simon comforts her. "Make them stop. They're everywhere. Every city, every house, every room, they're all inside me. I can hear them all, and they're saying nothing!" Jayne agrees, but finds the whole thing unnerving. "Everybody's dead. This whole world is dead for no reason!" They make their way to a beacon they noticed transmitting from up above.
In a very damaged building, River activates a recording. My favorite actor probably ever, but Top Five definitely, Sarah Paulson, appears in hologram. "These are just a few of the images we've recorded. And you can see it isn't what we thought. There's been no war here and no terraforming event. The environment is stable. It's the Pax. The G-Paxilon Hydrochlorate that we added to the air processors. It was supposed to calm the population, weed out aggression. Well, it works. The people here stopped fighting. And then they stopped everything else. They stopped going to work, they stopped breeding, talking, eating. There's a million people here, and they all just let themselves die." Crashes sound outside the image, screaming, Reavers. "I have to be quick. About a tenth of a percent of the population had the opposite reaction to the Pax. Their aggressor response increased beyond madness. They have become...well, they've killed most of us. And not just killed -- they've done things." The crew realizes what happened. "I won't live to report this, but people have to know. We meant it for the best to make people safer." She holds a gun to her head, but a Reaver appears and drags her out. Jayne begs, "Turn it off." River falls to the floor, vomits. Simon drops to her side, but she protests. "I'm all right." She considers the secret she's been holding, the toxic truth that has made her insane. "I'm all right."