'Shock Corridor'

Directed by Samuel Fuller, himself a veteran of World War II when he took part in the landings in Africa, Sicily and Normandy in addition to helping liberate a concentration camp, it's a story of a journalist, who fakes incest with his sister (actually his stripper girlfriend), to get admitted into a mental hospital to investigate the murder of a patient.

With his eyes on the Pulitzer Prize, the journalist sinks deeper and deeper into the psychosis of his fellow inmates as they attempts to break down their mental issues to find out who killed the patient.

Meanwhile, his own mental health is waning in his mania and he begins losing connection with reality. He actually starts thinking his girlfriend is his sister.

In the end, he finishes his story and blows the lid off the murder. However, his digging wound up burying his mind and he becomes a permanent resident of the mental ward.