Butcher, Baker, Nightmare Maker (1981)

What it's about

Rejected by her lover, the only man left in Cheryl's life is the orphaned nephew she has raised as her own son. She'll stop at nothing to keep Billy with her. When her plans misfire, she is swept up into an insane frenzy that means death to anyone who comes between her and her obsession. But the investigating detective is convinced that Billy is the real killer - and determined to prove it. Madness and fanaticism work together to drag all concerned into a terrifying vortex of blood-letting that adds a nightmarish twist to the classic Oedipus story.