Based on an Oliver Sacks case study, Dr P is a baritone opera singer who cannot distinguish his students until they speak. He suffers from visual agnosia, more specifically prosopagnosia, which only allows him to see details that he must cognitively assemble to identify an object. For example, he can describe a rose as a "convoluted red form with a linear green extension," but can only identify it as a rose by smell. Dr S, the neurologist, examines him, first in a clinic, then in his home environment, and deals with Dr P's concerned wife, culminating in a heated argument about whether Dr P's paintings are abstract art or the result of his occipital degeneration. Dr S only learns how Dr and Mrs P cope with the situation, but cannot diagnose the situation. The opera, filmed cinematically on locations and sets and not on a theatrical stage, is intercut, sometimes jarringly, with footage of Oliver Sacks reflecting on his encounters with Dr P, as well as scenes of a pathologist examining the real Dr P's brain, identifying his condition as a rare but not unique symptom of Alzheimer's, for until near the very end his only symptoms were strictly occipital, suggesting, perhaps, a tumor. This material, which is sometimes redundant, gives the film the effect of a documentary with staged reenactments, only the reenactments are operatic rather than standard non-musical drama.