Twin sisters Clara and Dempsey have always struggled to relate, their familial bond severed after their mother vanished into the Thames. As infants they were adopted into different families. In adulthood, they are content to be all but estranged, until Clara sees a woman who looks exactly like their mother on the streets of London. The catch: this version of Serene, aged not a day, has enjoyed a childless life --- the very life, it seems, she might have had if the girls had never been born. As with most things, Clara and Dempsey cannot see eye to eye on the confounding appearance of this woman. Clashing over this stranger who burrows deeper and deeper into their lives, the sisters hurtle toward an altercation that threatens their very existence, forcing them to finally confront their pasts --- together.