Helen Quilley (Gwyneth Paltrow) gets fired from her public relations job. As she leaves the office building, she drops an earring in the lift and a man picks it up for her. She rushes for her train on the London Underground and misses it. The plot then splits into two storylines, presented as Parallel universe (fiction)s, in which different events ensue, consequent upon whether or not she catches a particular train.