It’s 1921, and Florence Cathcart (Rebecca Hall) is doing brisk business as an author and professional ghost chaser. She never actually catches any spirits though because her specialty is in disproving their existence. Using a combination of common sense, high (and low) tech gadgetry and deductive reasoning she debunks charlatans and identifies the true causes behind supposed hauntings. Post-WWI England is a country still reeling from the loss of over a million lives. The war and the cruelty of influenza have left behind millions more mourning their loved ones and ripe for exploitation at the hands of so-called mediums and psychics. Cathcart relishes the moment when she reveals them as liars and thieves even if some of the customers prefer the fakery as a form of comfort. But each unveiling of the truth also comes with a tinge of sadness for her. She doesn’t believe in the afterlife, but that doesn’t mean that some small part of her doesn’t wish it existed. When Robert Mallory (Dominic West) appears, wanting her help investigating recent ghostly sightings at a boys boarding school in the countryside, her instinct is to say no, but she eventually accepts the opportunity to expose yet another fraud. Her expectations of man-made shenanigans are quickly met. And then the real ghosts arrive.