For the troubled, unpredictable Marina (Anna Friel), with her glamorous father and valium addicted mother, Holly (Michelle Williams) is the only constant in her life. For Holly, Marina represents sex, drugs and rock'n'roll, a stark contrast to her own insecurity over her appearance and studious lifestyle.

As the years roll by, the girls experience all life has to offer - sex, love and loss - but the whole while Holly harbours a secret passion for Marina's brother, Nat (Oliver Milburn). Eventually the truth comes out, and the friendship, which has never been equal, becomes a trap, and Holly must decide whether she wants to find the courage to live her life without her best friend.