As Andy Barclay endures intense therapy sessions with the possessed head of Chucky, a parallel story unfolds with Nica Pierce, portrayed by Fiona Dourif. Confined to a mental institution for four long years, Nica has been wrongly accused of murdering her family under Chucky's sinister influence. Convinced that she is the real culprit and that Chucky merely symbolizes her psychosis, she is transferred to a medium-security psychiatric hospital, where she comes under the scrutiny of Dr. Foley. Within this therapeutic environment, Nica meets a diverse group of patients: Malcolm, battling dissociative identity disorder; Angela, who believes she has already crossed to the other side; Claire, a firestarter; and Madeleine, a woman tormented by the memory of having smothered her own child. As Dr. Foley introduces a controversial therapy method using Good Guy dolls, all but Madeleine are visibly disturbed, with her treating the doll as if it were her lost child.
Nica's world turns tragic when Tiffany Valentine, played by Jennifer Tilly, comes bearing sorrowful news: her niece Alice has died. Stricken with grief, Tiffany leaves a Good Guy doll as a parting gift from Alice, deepening Nica's turmoil. Later that night, as Nica struggles with her thoughts, Chucky awakens and discovers that she attempted to end her own life. The following day, Nica awakens to a horrifying sight: Angela's lifeless body, thus shattering any remaining illusions about her sanity. As she connects the dots, Nica realizes that Chucky is not just a figment of her imagination, especially when she learns that "Valentine" is Chucky's girlfriend's surname.
In a desperate attempt to combat the growing threat, Nica reaches out to Malcolm, but his warning to Madeleine only leads to chaos as both the doll and Malcolm find themselves buried alive. Nica’s harrowing situation intensifies when Malcolm starts referring to himself as "Charles," mimicking Chucky’s nefarious traits. Tragedy strikes when Claire meets a gruesome fate as she is decapitated by Chucky.
Simultaneously, Andy uncovers the chilling truth behind the murders: Chucky has managed to transfer his evil spirit into multiple bodies. Seeking clarity, Nica agrees to undergo hypnosis with Dr. Foley to unearth repressed memories related to the gruesome events. However, their session is abruptly interrupted by Chucky, who cleverly manipulates Dr. Foley into believing that Nica is the aggressor, leading to a sinister game of blackmail.
Madeline's inner turmoil spirals as she grapples with her grief, resulting in an act of desperation towards her Good Guy doll, and soon thereafter, Nica's mental state begins to destabilize as she is lured into the institution's chaos. In a dramatic twist, the dolls’ malevolence escalates; Madeleine’s doll comes to life, leading to Foley's demise, and splitting its soul, thus intensifying the horror as Chucky awakens and orchestrates a malicious plan to further extend his reign of terror.
As the chilling events unfold, relationships shatter, and the mortal coil of the characters hopelessly intertwines with Chucky’s sinister motives. In a shocking revelation, Nica, now possessed by the spirit of Foley, regains her mobility and exacts vengeance by brutally killing Dr. Foley. Amidst the escalating mayhem, Malcolm's dark secrets are revealed, leading to his untimely end at the hands of Madeleine's doll. Chaos reigns as Andy confronts the reality of his situation and is forced into self-preservation against Nica, but finds himself trapped with dwindling options.
In a climactic exchange, Nica, now an amalgamation of the malignant force within, escapes with Tiffany, sharing a fleeting moment of liberation before venturing into a grim future with another Tiffany doll that carries a fragment of her essence. Meanwhile, in the haunting post-credits scene, Andy's past returns to haunt him as his former foster sister, Kyle, cunningly infiltrates his home, intent on continuing the macabre saga instigated by Chucky's disembodied head, symbolizing the eternal darkness that has plagued Andy for so long.
