When Edna mysteriously vanishes from the town of Creswick, her daughter Kay and granddaughter Sam arrive to look for her. As Kay discovers mounting evidence her mother is suffering from dementia, creeping dread turns to sheer panic – Edna could be anywhere.
Kay is overcome with guilt; Edna had called her several weeks prior, fearful there was an intruder coming into her house. Did Edna simply wander off and get lost, or was she taken? When Sam and Kay start to notice eerie and mysterious happenings around the house, they begin to fear the latter.
Suddenly, as inexplicably as she disappeared, Edna returns; with no memory of the past several days, or at least none she's willing to share. Initially there comes a wave of relief, but Edna's unsettling behaviour makes it clear she can no longer manage living on her own. Kay, haunted by her guilt and childhood nightmares of a mould-infested cabin and elderly relative abandoned in it many years ago, is faced with a difficult decision about whether to move her mother into an aged care facility. Sam won't support the idea and instead decides to move in with her Gran to look after her full-time. What Sam sees as a selfless act, Kay thinks is naïve, and mother and daughter are pulled further apart.
While Kay travels to Melbourne to take a tour of a retirement village, Sam discovers caring for Edna is more challenging than she first envisioned. Edna is prone to sudden, almost violent outbursts and worse, seems to be... changing. Is this simply the horrors of dementia or is something more sinister at play?
Disturbed by her Gran's swings in behaviour and in an effort to understand what's going on, Sam visits her neighbour and learns Edna had aggressively locked young Jamie in her closet. Returning to investigate, Sam discovers a cramped, seemingly endless labyrinth within the walls of the house and is hit with a jarring realisation: is this where Edna went missing? Sam then becomes trapped in the claustrophobic, moulding maze herself.
Meanwhile, Kay has made a decision, she wants to make amends and care for her aging mother. Edna, in a lucid moment, agrees to return to Melbourne.
Things unravel when Kay, horrified, later discovers Edna locked in the bathroom shedding her skin, revealing a moulded flesh underneath. Alarmed, Kay follows Edna into the labyrinth within the walls, where Edna quickly turns savage and monstrous. Kay's guilt-riddled nightmare is coming to life as Edna sheds more and more skin, further exposing a blackened, skeletal creature within.
Amidst the horror in the walls, Kay is reunited with Sam as they both fight to survive and reconnect as mother and daughter. After violently attacking the monstrous form that is Edna in an attempt to protect Sam, Kay unexpectedly discovers the creature underneath is not what she thought...and that if she is to end the sinister manifestation of dementia that has its grips on her family, she must come face to face with what has been abandoned for too long.