Lock.

Head guard Hamza and his team conduct a headcount every morning at the prison. One day, during a routine check, they find one or two bodies in each cell they enter. There are no signs of beating, injury, or strangulation on the bodies of the ten prisoners found dead in eight cells. The other prisoners in the cells also make no statement about the incident. Selin Korkmaz from the intelligence agency and Chief Inspector Erol Haktan from the homicide department are assigned to investigate the incident. The two begin their investigation by quarantining the prison and questioning everyone inside. As Erol and Selin meticulously investigate every detail to solve the mystery of the murders, they uncover shocking truths with each "lock" they open.