The story is set in the near future, where the government has to implement a "one-child" policy due to overpopulation and famine. Because of this strict family planning agenda, the sisters must take turns using the identity of one person, Karen Settman (Rapace). Their grandfather (Dafoe) named them Monday, Tuesday, Wednesday, Thursday, Friday, Saturday and Sunday. Everyone can go out once a week. The sisters can only live freely in their own apartment. Until one day, "Monday" didn't come home...