The Guardian

Diana, posing as the nanny, abducts the Sterlings' infant daughter and lures her into a forest ritual. She leads the child to the base of a giant, gnarled tree where the sacrifice is performed to sustain the tree's life. As the ritual unfolds, Diana's reflection in a pool morphs into a growling wolf. This act establishes the dark power behind the nanny's façade.

Three months pass and Phil and Kate Sterling relocate from Chicago to Los Angeles as Phil takes a lucrative advertising job. Kate discovers she is pregnant and later gives birth to their son, Jake. In an effort to balance work and family, they hire a nanny to help with Jake and the house. The household settles into a routine that will soon be disrupted by darker forces.

The Sterlings interview two candidates, Arlene and Camilla. Arlene dies in a bicycling accident, and Camilla is swiftly hired to replace her. Camilla proves to be an invaluable addition to the household, earning the family's trust with warmth and competence.

Camilla rests with Jake in a meadow when three aggressive bikers try to assault her. She flees to the base of the gnarled tree, which suddenly comes to life and begins strangling the men. Wolves arrive and feed on the scene as the tree's power is revealed.

During a later dinner, Ned invites Camilla on a date, which she declines. That night, Phil dreams of having sex with Camilla, blending fear and desire in his subconscious. The couple's trust in Camilla begins to waver as strange tensions rise.

Ned returns to the house with flowers for Camilla, but she has left on foot. He tracks her to the forest and discovers Camilla bathing in a creek, approaching the tree and fusing with its bark. A pack of wolves then invades the home, and Camilla appears on the hearth, having killed Ned and dragged his remains away.

Phil checks the answering machine and finds a message from Molly Sheridan urgently asking to speak with him about the nanny. The next message is Ned's incoherent voicemail, which Camilla quietly blocks from being fully heard. The twin messages set a chill about Camilla's true identity.

Phil meets Molly, who describes the disappearance of her infant daughter and reveals Camilla as the nanny they later discovered to be a false identity. She asks Phil to arrange a meeting with Camilla to confirm her suspicions. Phil begins to suspect Camilla and shares his concerns with Kate.

Phil listens to Ned's warning about Camilla and discovers Ned is missing. The mounting evidence suggests Camilla may be at fault, heightening the couple's fear. The couple prepares to protect Jake as the threat grows.

Jake falls into a coma-like state as tension with Camilla escalates. Camilla attempts to kidnap Jake, but Phil intercepts her and knocks her to the ground. The crisis drives Kate and Phil to retreat toward safety while the threat of Camilla remains.

Phil and Kate flee with Jake as wolves converge on the home. Camilla pursues them, levitating through the forest toward the giant tree. Kate drives the Jeep in a bid to escape, and Phil carries Jake toward safety as Camilla closes in.

Kate crashes into Camilla with the Jeep, seemingly killing her. Phil examines the tree and notices baby faces embossed in the bark, confirming the tree's sinister nature. A detective later confirms there is no evidence of Camilla's existence.

Phil returns home to his battered family as Camilla, now part-tree, infiltrates the house again. He and Kate fight to protect Jake while the living tree bleeds as branches entangle them. Phil finally fells the tree with a chainsaw and Camilla's body disintegrates as the tree combusts, leaving the family safe at last.