Rory and Amy get the Doctor's attention by making crop circles in their hometown. When he shows up, he's met not only by the Ponds but also by their friend Mels. She's sassy and wears beaded braids and has been best buds with Amy and Rory since childhood. Having grown up listening to Amy's stories, Mels seems quite cross about the Doctor, a man she's come to blame for all history's greatest tragedies. She forces her way onto the TARDIS at gunpoint and then suggests they all go kill Hitler.
Also out to do away with the Fuehrer is a futuristic crew from some Justice Department. They members have shrunk themselves to control a shape-shifting robot from the inside, and disguised it as some random Nazi. Just as the random Nazi robot is about to kill Hitler, the TARDIS materializes and everything goes to hell. Naturally. The Doctor's a bit squeamish about inadvertently saving Hitler's life, so he has Rory just stuff the guy into a cupboard. There he remains for the rest of the episode. Meanwhile, Mels has been fatally injured in the craziness. Except she doesn't die, because she's actually Melody Pond and she regenerates into the River Song we've come to know and love. Except she doesn't know who River is at this point. Having been brainwashed by the Silence all her life, she wastes no time in kissing the Doctor with some poisonous lipstick. He's doomed to die in minutes, with no prospects of regenerating... for some reason.
The Justice Department sets its sights on River, who's apparently an even bigger target than Hitler thanks to her future killing of the Doctor. Amy and Rory rush off to save her and get shrink-rayed into the shape-shifting robot. The Doctor, although flailing about from his poisoning, is hellbent on saving them and River. He does, of course, but he can't save himself and soon expires. The Ponds finally tell their childhood friend the truth about River. River, somehow overcoming years of brainwashing, brings the Doctor back to life by using up all her regenerative abilities. It's all very rushed and very confusing and kind of good in places. I'll try to sort it out in the Weecap.
Much like the episode's miniaturized robot operators, the Doctor Who coverage has been shrunk from recap to weecap. If I skip over something vital or seem to forget important details, or rewrite events entirely, just pretend I'm imitating one of the show's writers. Here we go!
Amy and Rory are driving through a wheat field at breakneck speed. Tense music plays. Amy shouts instructions at Rory with great urgency. Turn right! Turn left! Loop the loop! Finally, she yells at him to stop and they find themselves in a circular clearing, at the middle of which is the TARDIS and the Doctor. He holds up an aged newspaper to show them the headline: "Leadworth's Crop Circle." The camera zooms up and shows the Doctor-shaped message they've carved into some poor farmer's crop. Amy wants to know if he's found Melody. He hugs her (with Rory's "permission" -- ugh) and reminds her that she knows who Melody grows up to be, so she knows he'll find her. About then, they all realize that someone is speeding through the field in a hot red Corvette and very symbolically crossing out the "Doctor" message. The Doctor and friends scream and scatter just as the Corvette skids to a stop beside the TARDIS.
A gorgeous young woman steps out, played by Nina Toussaint-White. She's got on leather boots and vest to match and her hair's all in tiny braids. She stands over the Doctor. "You said he was funny; you never said he was hot." The Doctor is a bit aghast that this little detail was left out. Rory and Amy call her "Mels" and worry she'll go to prison one day for stealing cars and what have you. She fondles the TARDIS and seems pretty turned on by the whole concept of time travel. "I'm their best mate," Mels says to the Doctor, explaining she's heard a lot about him. "Then why don't I know you?" asks the Doctor. "I danced with everyone at [Amy and Rory's] wedding!" "I don't do weddings," Mels says. And this show don't do continuity. Mels hears police sirens drawing near and pulls out a gun. She points it at the Doctor and hijacks herself a ride out of there, saying, "You've got a time machine, I've got a gun. What the hell? Let's kill Hitler."
But first, let's go visit the past, when little Amelia and little Mels were bestest buds. "Is he hot?" Mels asks as they play in Amelia's bedroom. "No, he's funny," says Amelia. She clearly thinks he's hot later. Maybe puberty hasn't hit yet. A very small boy comes in. It's Rory and he's moping because the girls haven't made much of an effort to find him in their game of hide-and-seek. Oddly, he looks a lot younger than the girls. Then there are some flashbacks to their school days when Mels blames the Doctor for the Titanic's sinking and Hitler's rise to power simply because he didn't intervene. Moving on to their teen years, Rory and Amy chastise Mels for stealing a bus. Mels changes the subject by trying to nudge Amy and Rory together in a romantic way, but Amy scoffs. She's not against the idea, mind you, but she thinks it's impossible because, as she says, Rory is gay. He's never paid any attention to a girl, she says. He gapes at her and looks like he's peeing himself before he finally flees the scene. Amy realizes all this time he's only had eyes for her. Luckily, by this point, he doesn't look half her age anymore.