On a secluded farm in a nondescript rural town, a man is slowly dying. His family gathers to mourn, and soon a darkness grows, marked by waking nightmares and a growing sense that something evil is taking over the family.
The Dark and The Wicked follows two siblings who are summoned back to the family farm to await the inevitable death of their father. What initially appears to be a timeless ritual of loss and remembrance turns out to be something very different.
Louise and Michael are siblings who are brought back to their family farm in Texas when their father's illness, which keeps him bedridden and uncommunicative, cared for by his wife and a nurse, worsens. Their mother seems disturbed and expresses a desire for the children to leave. At night, she hangs herself in the barn after cutting off her own fingers in the kitchen.
As time goes on, Louise and Michael start to understand what happened to their mother. The nurse confides in them that she heard her whispering to the father, but it seemed as if she was speaking not to him, but some other presence. Michael finds their mother's diary, which describes her fears of an unnamed and possibly demonic presence preying on her husband.
At their mother's burial, Louise and Michael meet Father Thorne, a priest who claims to have known their mother. Later that night, Father Thorne appears at the farm, beckoning them from outside, before vanishing before their eyes. Meanwhile, Charlie, a ranch hand who lives on a nearby plot of land in his RV, witnesses a vision of what appears to be Louise, speaking indistinctly and cutting herself repeatedly with a kitchen knife. The entity drives a distraught Charlie to shoot himself in the head with his shotgun.
Louise is subsequently unable to reach Charlie by phone, unaware that he is dead. Louise calls the phone number that Father Thorne gave her to ask why he visited the farm the night prior. The man who answers claims to have never met her, and says that he lives in Chicago and has never been to Texas. Worried for their father's safety, the siblings summon a doctor for a house call and request that he be moved to a hospital. The doctor determines that their father's health is grave, and that he is on his deathbed. He tells the siblings he cannot relocate him to a hospital, as moving him could result in him dying en route.
On the farm, Louise and Michael find that their large herd of goats have all been brutally killed. The two start a bonfire to dispose of the numerous animal carcasses. That night, Michael is approached in the barn by an apparition of his nude mother, who disappears as she approaches him. Later, while Louise lies in bed beside her father, she has a nightmare in which the entity attempts to possess her, but she manages to resist it, before witnessing her father levitating against the ceiling.
In the morning, Charlie's granddaughter arrives at the farm and informs Louise that he killed himself two days prior. The girl's forlorn demeanor soon turns malevolent, and Louise realizes it is in fact the entity taking the shape of Charlie's granddaughter. She too disappears before Louise's eyes. The nurse arrives moments later to care for Louise and Michael's father. Meanwhile, Louise finds that Michael has fled the farm to return to his wife and daughters, leaving her behind. Michael calls Louise from his cell phone, and tells her she too should leave. Moments later, the nurse, possessed by the entity, begins stabbing herself with a pair of sewing needles, attacking Louise in the process, before stabbing herself in the eyes, killing herself.
Michael arrives at his home and finds the dead bodies of his daughters and wife in the kitchen, in what appears to have been a murder-suicide. A distraught Michael cuts his own throat, and moments after, observes that the bodies of his wife and daughters have disappeared. He realizes the entity has tricked him when his wife and daughters enter the house moments later, and find him bleeding to death.
Back at the farm, Louise regains consciousness at nightfall and finds that her father is dying. Moments after he dies, the demon in turn attacks and claims her.
