While it's certainly true that the concept of inmates taking over the asylum is nothing new, it's hard to think of a better variation on the formula than this.
Ray Milland plays Dr. Howard Fennick, a former psychologist whose cool, polished exterior (almost) conceals the fact he's also a homicidal maniac who was committed for murdering his wife.
His current delusion is that he's "assisting" the real head of the asylum, Dr. Norton, whom he accuses of keeping him there out of sheer laziness, so Fennick can do his job for him. When Norton refuses to release him, Fennick murders the doctor and somehow manages to imprison the rest of the staff. With other inmates filling the roles of orderly, nurse and cook, Fennick is eager to put into practice his own notions of treatment for the mentally ill, when the unexpected arrival of Dr. Norton's niece Natalie (Claire Griswold) threatens to put a kink in his plans.
Relieved to find that Natalie has never met her uncle, Fennick pretends to be Dr. Norton, graciously inviting her to consider his asylum her "home away from home".
And from then on, of course, it's only a matter of how long it will take Natalie to realize the true nature of her predicament, as the only sane person trapped in a madhouse run by a madman. Along the way, we're treated to a satisfyingly sinister performance by Milland and a story tinged with black humor, containing some nasty twists for the increasingly desperate heroine, all propelled by a tense and evocative Bernard Herrmann score. An outstanding entry in this TV series.