A young orphan and outsider, Sarah (Tatiana Maslany), gets off a commuter train one day and sees someone who looks just like her on the opposite platform. In the next moment, Sarah’s double commits suicide. Sarah decides to take advantage of this coincidence and plans to use her looks for financial gain. She ends up assuming her identity, her boyfriend (Dylan Bruce), and her bank account. But instead of solving her problems, the street smart chameleon is thrust headlong into a kaleidoscopic mystery. She makes the dizzying discovery that she and the dead woman are actually clones. Are they the only ones? Sarah quickly finds herself caught in the middle of a deadly conspiracy. With an assassin hot on her trail, she must race to find answers about who she is and how many others there are just like her.