A well-mounted period horror tale, The Asphyx (known also as Spirit of the Dead) focuses on the scientific endeavors of Robert Stephens, whose revolutionary work in the burgeoning field of photography leads him to the remarkable discovery of the title creature -- a soul-stealing demon known to Greek myth which appears at the moment of death to carry the soul away from the body and into the netherworld. By using special lighting techniques, he is able to detect the demon when it appears to steal the soul of a guinea pig, and he manages to capture it in a sealed capsule -- thus rendering the animal immortal. Realizing that the act of imprisoning his own asphyx will grant him eternal life, Stephens starts re-creating his experiment with human subjects. As this is a horror film, his new effort doesn't turn out quite as planned.