A film which follows one persons life, however in two different situations.
At the start, there is an insignificant action which splits her life. As a viewer, we follow both paths simultaneously - the one she's living, and the one which had she been a second earlier, her life would have took.
The instance which divides her life is the cliche not-getting-on-the-train-in-time. She was just a second too late meaning she had to wait for the next one.
This resulted in her being late for work, and being fired, and then going home to find her boyfriend cheating on her...before then meeting a guy who she ends up dating.
Had she been a second earlier, she would have made it to work, although would still be oblivious to the fact her boyfriend was cheating on her, and basically this followed a totally different direction.
So this story is all about the what if's, and this film carries out the if in parallel to what is really going on.