After a young man is killed in an unexplored subterranean cavern and his girlfriend driven mad by something she saw there, a track found at the scene cannot be identified with any known animal and thus a scientific expedition is launched to find out just what it is that is living there.
as Profesor Díaz
as Dr. Pena
as Hilda Ramírez
as Jaime Rocha
as Laura Ponce
as Dr. Manuel Ríos
as Julia
as Apolinar
as Novio de Julia
as Gerente de gruta (uncredited)
as Padre de Julia (uncredited)
as Turista (uncredited)
as Psiquiatra (uncredited)
