A psychiatric inmate, David Hoyle, is the clear culprit in the fatal stabbing of a nurse at Blackhill Asylum. When Chief Superintendent Matthew Lawson and Police Surgeon Dr Lucien Blake arrive at the crime scene, Hoyle is having electro convulsive therapy.
Still confused after the shock treatment, Hoyle tells Blake and Lawson he thinks he killed nurse Violet Ashby but cannot recall the incident. Lawson says Hoyle was found crouched near the body holding a large kitchen knife. However Dr Blake is not convinced.
A voluntary patient at the institution, Oriel Vogel, surprises Dr Blake when she turns up unannounced at his surgery with a painting she's done of him. She has also done a moody portrait of David Hoyle, which interests Blake.
Back at the asylum Blake tests his theory in a rather unorthodox manner.
At home, Blake consoles his ego with a bottle of Scotch whisky and ends up terribly drunk. When Jean helps him to bed late at night, she takes the opportunity to read his private letters from Singapore. She finds a photo of Blake with his family, dated September 1940.