Katherine awakes in an underground cell with three other women - all have complete amnesia. The women soon discover they are part of a gruesome experiment with no obvious purpose. That night Jane witnesses the first visit to their cell by the terrifying figure of the blood splattered Surgeon. One by one the Surgeon cuts a four digit number into each woman's skin - the exact time he will return to kill them. Each woman must piece together the dark secret behind the experiment and survive the Surgeon's nightly visits of pain, torture and grisly murder. Is there any way to escape? What is the purpose of the experiment? And who or what is screaming every time the lights go out?