After landing on planet M-113, the Enterprise is stalked by a creature which can assume the shape and form of anyone it chooses and which kills by removing the entire salt content of its victims' bodies.
A recently widowed, ex-film star (Ida Lupino) attempting a comeback suffers traumatic incidents that parallel her early movies.
Solo, Kuryakin and Waverly turn a plain music student into a glamorous Parisian performer to trap a ring of diamond thieves.