It's several weeks before Christmas in Britain and veteran rocker Billy Mack (BILL NIGHY), with aid of his longtime manager, Joe (GREGOR FISHER), has rerecorded a Christmas version of his smash hit single. As it starts to play on the radio, the new Prime Minister (HUGH GRANT) takes office and immediately finds himself smitten with one of his staff workers, Natalie (MARTINE McCUTCHEON), when not standing up to the visiting President of the U.S. (BILLY BOB THORNTON).
There's a new woman in Karen's (EMMA THOMPSON) life, but she isn't pleased about a young and attractive worker, Mia (HEIKE MAKATSCH), who is coming on to her husband, Harry (ALAN RICKMAN). When he's not enjoying that newfound attention and trying to figure out whether he should act upon it, he tells Sarah (LAURA LINNEY) that she should act on her longtime crush of coworker Karl (RODRIGO SANTORO).
Speaking of crushes, it seems that Mark (ANDREW LINCOLN) has one on Juliet (KIERA KNIGHTLEY). The only catch is that she's the new bride of his best friend, Peter (CHIWETEL EJIOFOR). While movie stand-ins John (MARTIN FREEMAN) and Judy (JOANNA PAGE) end up falling for each other while rehearsing a graphic sex scene, young Sam (THOMAS SANGSTER) tells his recently widowed stepfather, Daniel (LIAM NEESON), that he's in love with Joanna (OLIVIA OLSON), the most popular girl in school.
After discovering his girlfriend cheating on him with his brother, writer Jamie (COLIN FIRTH) moves out and finds himself falling for his new Portuguese housekeeper, Aurelia (LUCIA MONIZ), despite neither understanding the other. And young Colin (KRIS MARSHALL) has decided to head off to America where he hopes his looks, personality and British accent will help him bed many American women.
As the days count down toward Christmas, the various characters prepare for the holiday as well as love and the various relationships in their lives.