Pig (Cillian Murphy) and Runt (Elaine Cassidy) born on the same day, in the same hospital, moments apart. Twins, all but by bloodline. Inseparable from birth, they are almost telepathic. They are one, needing no one else, inhabiting a delicate, insular and dangerous world where they make their own rules and have their own language. They are also partners in crime, with an appetite for recklessness, exploration and destruction. But days before their 17th birthday the perfect balance of their world begins to shift. Pig's sexual awakening and increasing jealousy begins to threaten their private universe. Unable to contemplate the loss of Runt, Pig's unpredictable nature spirals out of control in a trail of violence and destruction. The inseparable are about to separate, and which one will survive will depend on which one can break free.