Citadel

Tommy and his wife Joanne are moving out of a condemned tower block. While Tommy is stuck in the lift, a group of hooded teenagers assault Joanne, and the lift doors refuse to open. Tommy reaches her only to discover she has been beaten, and a syringe is found in her abdomen.

Joanne is rushed to hospital. Doctors manage to save the baby, but Joanne falls into a coma. Tommy is left to cope with the consequences and the fragile life of their infant daughter Elsa.

Tommy now lives in a run-down council estate with his baby daughter Elsa. He suffers from agoraphobia after the attack and is terrified to leave the house. He visits Joanne in hospice, where doctors say there is no hope of recovery, and consents to turning off life support; a nurse named Marie consoles him.

At Joanne's funeral, Tommy meets a foul-mouthed priest who warns that the gang will return for his daughter. The priest has a young boy, Danny, who is blind but seems to be able to perceive Tommy and his danger.

That night, hoodies break into Tommy's house, ransacking it and looking for Elsa. Tommy calls Marie for help, but the line cuts before he can explain. He spends the night barricaded in the bathroom with his baby, seeking safety as fear grips him.

Marie takes Tommy and Elsa into her home for a few days, trying to calm him down. She argues the youths may be victims of circumstance rather than a coordinated threat. Tommy insists on seeing the priest again and Marie offers to help.

The priest reveals an urban myth: a pregnant woman gave birth to twins in the tower block who grew up feral and blind, able to 'see' through sensing fear. They kidnapped children and became a mutant breed, including Danny, who was saved by the priest before he transformed. The tale suggests the tower has become a nest for monsters.

Tommy refuses to help, while Marie tries to reassure him. The next day, they head to the bus depot; in the badly lit underpass, Marie approaches the hoodies to prove there is nothing to fear. The hoodies attack and kill Marie, triggering Tommy's desperation.

Tommy flees with Elsa as ferals give chase. They board a bus, but it stops and hoodies swarm aboard, assaulting the driver and passenger, and beating Tommy to steal Elsa.

Tommy seeks the priest's aid. The priest reluctantly agrees to help only if they blow up the abandoned tower block. They go to the tower with Danny, who can mask their presence from the ferals.

Tommy is separated from the group when he hears a baby crying, setting a trap for him. The ferals descend and the priest sacrifices himself to save Tommy and Danny. Before dying, the priest reveals himself as the father of the original infected kids.

Tommy and Danny reach the basement to find Elsa safe, but there are other turned children in cages beyond help. The group realizes the horror that has grown in the tower.

Tommy leads Elsa and Danny toward the exit as the ferals block their way. Danny confesses he never had the power to protect anyone, but Tommy overcomes his fear and navigates through the group without being sensed. They push forward toward safety.

Outside, Tommy watches explosions destroy the tower block and its mutant inhabitants, ending the threat and freeing them. The destruction marks the end of the immediate danger to Elsa and the few remaining survivors.