It's Christmastime, which means that Earth is in danger again. This time, the danger falls from the sky in the form of little snowflakes that have teeth like piranhas. They land in England, in the year 1842. In what looks like an orphanage or something like it, several children run around and play and pelt each other with snowballs. One boy busies himself with building a snowman. A woman approaches him and asks, "Walter, don't you want to go play with the other boys and girls?" She worries that it's not normal, his refusal to talk to others. She sighs and goes inside. "I don't want to talk to them," he says to his snowman. "They're silly." His snowman agrees with him... out loud. Walter looks around, but nobody else is nearby. He's a bit freaked out, so he runs away. The snowman calls him back. "Don't need anyone else," it says. "I can help you." Intrigued, the boy walks slowly towards the snowman again. "How?" he asks.
The boy's cherubic face fades as 50 years pass, and is replaced by Richard E. Grant's severe scowl. This older Walter oversees two men as they scrape flakes off of snowmen and collect them in jars. Walter and the jars get into a carriage with the letters "GI" painted on the doors. They travel to an estate surrounded by a wrought iron fence bearing the same monogram. Walter brings a jar of snow into a spacious study and says, "The last of the arrivals has been sampled." He's talking to a giant gumball machine with bolts of electricity zapping around it. "The great swarm is approaching," says the gumball machine in the same voice as the long-ago snowman. He says humanity is at an end. "Will the final piece be ready?" it asks. "It's in hand," Walter says. The gumball machine is filled with swirling flakes. Walter adds one jar's contents to it. Then he goes outside to where a bunch of homeless men are waiting for a dinner he's promised them. "Dr. Simeon, it's getting late," one guy says to him. It turns out to be one of those "To Serve Man" situations and a horde of toothy, snarling snowmen pop up from the ground to eat all the poor hungry guys.
Cut to a cozy little tavern called the Rose and Crown. Viewers at home will recognize the pretty young barmaid as Oswin from the season premiere. For no apparent reason, she seems rather self-satisfied as she turns toward the camera, like she's peered through the fourth wall and now she's in on the secret. Also for no apparent reason, she brings a tray of drinks outside. It's not like there's going to be any al fresco dining in the snow. She notices a snowman standing there and frowns. "Did you make this snowman?" she asks a passing gentleman. "No," he says. It's the Doctor, dressed in the fashion of the time and exhibiting something of a Monty Burns hunch. He keeps walking, but stops when she says the snowman appeared out of nowhere. He takes a closer look at the snowman. "Maybe it's snow that's fallen before. Maybe it remembers how to make snowmen." She flirts with him a bit and says her name is Clara. He doesn't recognize her because he only saw her in Dalek form.