This crisp thriller makes quick business of illustrating one of film noir's more unsettling tenets, that in our society, morality is relative. A detective is the reluctant escort for a racketeer's contemptuous widow who is to appear as a witness against organized crime; various mobsters make it their business to see that she does not arrive alive. The film takes place almost entirely within the narrow margins of a locomotive's interior, which cinematographer George Diskant (who shot Nicholas Ray's On Dangerous Ground and They Live by Night) turns into a glistening noir setting for fast turns and cruel deceptions.