Blackwater is the saga of a small town, Perdido, Alabama, and Elinor Dammert, the stranger who arrives there under mysterious circumstances on Easter Sunday, 1919. On the surface, Elinor is gracious, charming, anxious to belong in Perdido, and eager to marry Oscar Caskey, the eldest son of Perdido's first family. But her beautiful exterior hides a shocking secret. Beneath the waters of the Perdido River, she turns into something terrifying, a creature whispered about in stories that have chilled the residents of Perdido for generations.

When Margaret and her husband Hal bought the large Victorian house on Hawthorn Street—for sale at a surprisingly reasonable price—they couldn’t believe they finally had a home of their own. Then they discovered the hauntings. Every September, the walls drip blood. The ghosts of former inhabitants appear, and all of them are terrified of something that lurks in the basement. Most people would flee. Margaret is not most people. Margaret is staying.

Eric Ross is on the run from a mysterious past with his two daughters in tow. Having left his wife, his house, his whole life behind in Maryland, he's desperate for money—it's not easy to find steady, safe work when you can't provide references, you can't stay in one place for long, and you're paranoid that your past is creeping back up on you.

Episode Thirteen takes them to every ghost hunter's holy grail: the Paranormal Research Foundation. This brooding, derelict mansion holds secrets and clues about bizarre experiments that took place there in the 1970s. It's also famously haunted, and the team hopes their scientific techniques and high tech gear will prove it. But as the house begins to reveal itself to them, proof of an afterlife might not be everything Matt dreamed of.

In 1919, Kitty Weekes, pretty, resourceful, and on the run, falsifies her background to obtain a nursing position at Portis House, a remote hospital for soldiers left shell-shocked by the horrors of the Great War. Hiding the shame of their mental instability in what was once a magnificent private estate, the patients suffer from nervous attacks and tormenting dreams. But something more is going on at Portis House—its plaster is crumbling, its plumbing makes eerie noises, and strange breaths of cold waft through the empty rooms. 

This forest isn't charted on any map. Every car breaks down at its treeline. Mina's is no different. Left stranded, she is forced into the dark woodland only to find a woman shouting, urging Mina to run to a concrete bunker. As the door slams behind her, the building is besieged by screams. Mina finds herself in a room with a wall of glass, and an electric light that activates at nightfall, when the watchers come above ground. These creatures emerge to observe their captive humans and terrible things happen to anyone who doesn't reach the bunker in time. 

It’s 1923, and at Thistlecrook House, a forbidding home on the Scottish border, the roaring '20s seem not to have arrived. But Simon Christie has - a young man who can’t believe his luck when he gets a job cataloguing the infamous art collection of the Mordrake family. Yet from the moment he gets off the train at the deserted village station he can’t shift a headache and a sense that there’s more to the house and its gruesome selection of pictures.

There is much that heavily pregnant Grace still doesn't know about her new husband King's background. So, when word comes that King's father is dying, Grace is eager to accompany him to his childhood home, Blackwater, located in a remote part of Tasmania. Things go badly from the start. The house is in terrible repair, King's dying father yells at Grace to leave and King's twin sister, Ruth, seems disturbed by Grace's presence. After his father's death, King convinces Grace they must stay and help Ruth settle the estate, but as time stretches on he grows strange and distant.

During a midnight journey snaking through the Carpathian Mountains, these are the words whispered to Cath Fenwick. It is the warning she will later wish she'd taken more seriously. When Cath receives her invitation to The Event - a monetised retreat for social media influencers - she can't believe her luck. Irene Jobert is the most famous influencer in the world and now Cath will be one of the five participants chosen to stay with Irene in a renovated Transylvanian monastery.

Despite the uncomfortably claustrophobic quarters and rapidly dropping temperature, Christa believes they'll be safe as they wait out the storm. She couldn't be more wrong. Deep in the night, their tour guide goes missing...only to be discovered the following morning, his severed head impaled on a tree outside the cabin. Terrified, and completely isolated by the storm, Christa finds herself trapped with eight total strangers. One of them kills for sport...and they're far from finished.