Ann quickly reveals that she has a special interest in the family's youngest member, a seemingly mentally impaired adult man in his 20s who does not have a name and is called only "Baby".

Ann wants to work with Baby, who still acts and is treated like an infant by his mother and two sisters, thinking that with the proper treatment he might begin to behave more appropriately for his age group.

Eventually, goaded by pictures that Ann sent of Baby doing "adult" things such as standing, the Wadsworths break into the house with murderous intent.

She stabs Baby's two sisters, then buries Mrs. Wadsworth alive (alongside the corpses of her daughters) beneath the floor of a swimming pool that Ann had been building in her yard.

[7] "A bizarre drama of family dysfunction, The Baby was one of three theatrical features directed by Ted Post and released that year—the other two being Dirty Harry sequel Magnum Force and The Harrad Experiment, based on a once-controversial best seller about what happens when attractive college students are placed in coed dorm rooms.

[12] TV Guide awarded the film three out of five stars, calling it "Competently directed", and stated "despite its occasional lapses into genuine bad taste is fairly effective and contains a truly surprising twist ending.