流浪的孤儿Sarah（塔提阿娜·玛斯拉尼 Tatiana Maslany 饰）目睹一个女人自杀，因为与死者长的极为相似，遂决定假冒死者的身份领取一笔数目可观的存款。然而Sarah万万没有想到，自己竟然闯进了一个危险的谜局。在“扮演”死者的同时，Sarah发现了一个惊人的事实：她和自杀的女人其实都是克隆人，而且这批克隆人不止她们两个。不法组织为了达到不可告人的目的，创造了一批克隆的胚胎并将她们植入毫不知情的普通夫妻体内，让她们在不同的环境中出生、成长。没有人知道是谁创造了这些克隆人，也没有人知道他们的最终目的。这些克隆人必须尽快查明真相，否则一切都晚了，因为一个刺客正在将她们一个一个暗杀。SPOILER: Orphan Black follows outsider, orphan and street-wise chameleon Sarah. After witnessing a woman's suicide, Sarah assumes the stranger's identity - who happens to look just like her. Expecting to solve all her problems by cleaning out the dead woman's savings, Sarah is instead thrust headlong into a kaleidoscopic mystery as she realizes the dizzying truth - she and the dead woman are clones. As Sarah searches for answers, she discovers the chilling fact that there are more people like her out there - genetically identical individuals who were planted in unsuspecting birth parents and nurtured in completely different circumstances. With no idea who created the clones, she'll need to discover the reason in a hurry as an assassin is killing them one by one.