Will Freeman (HUGH GRANT) is a self-absorbed, shallow and single playboy who has few cares in the world thanks to continuous royalties from a Christmas song his father wrote decades earlier. A self-described "island," Will prefers to live a solitary life except when he's on the prowl for some female companionship.
After a married friend sets him up with Angie (ISABEL BROOK), a single mom who ends up breaking up with him rather than the other way around, Will decides to pursue single mothers for the passionate sex, ego massaging and easy breakups. That way, he eliminates the potential of the dreaded commitment.
It's when he's dating Suzie (VICTORIA SMURFIT) that he meets her friend's 12-year-old son, Marcus (NICHOLAS HOULT). A loner with few friends who's always picked on at school especially for unknowingly breaking into impromptu bouts of singing decidedly out of date songs, Marcus accompanies Will and Suzie for a day due to his depressed mom, Fiona (TONI COLLETTE), needing some time for herself.
Marcus takes a liking to Will and his ways, and after his mom attempts to commit suicide, the boy decides the playboy could be the man to make her happy. Although Will eventually starts dating another single mom, Rachel (RACHEL WEISZ), instead, he eventually and somewhat begrudgingly befriends Marcus. As he tries to help the boy cope with and/or overcome his social problems and awkwardness, Marcus unknowingly helps Will grow up and eventually become a more responsible person.