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Charlotte Ritchie as Alison Cooper – a young woman who has inherited a mansion from Heather Button, a distant relative of unspecified relation. After a temporarily death-inducing experience caused by Julian pushing her out of a window, she is able to see, hear and interact with ghosts.
Kiell Smith-Bynoe as Michael 'Mike' Cooper – Alison's husband, who has grand plans for the house but is not adept at putting them into action. Although at first believing the ghosts to be Alison's hallucinations, Mike comes to accept them and often tries to communicate with them despite being unable to see them.
Lolly Adefope as Katherine 'Kitty' Higham – an excitable, overly chummy, naïve Georgian noblewoman who wishes to be friends with everyone. She has repressed her unhappy memories of her adoptive family, particularly those of her sister. She died from the bite of a venomous spider concealed on an imported pineapple in 1780. As she is the only main ghost who is not white, some reports have speculated that the character may be inspired by the real-life story of Dido Elizabeth Belle.
Mathew Baynton as Thomas Thorne – a melodramatic and easily infatuated Regency Period Romantic poet, who was fatally shot in a duel in 1824. He falls in love with Alison at first sight.
Simon Farnaby as Julian Fawcett MP – a poltergeist, he is the most recently deceased ghost. A disgraced Tory MP who died of a heart attack in a 1993 sex scandal while not wearing trousers, he can physically interact with the corporeal world to a limited degree if he concentrates hard enough, typically with only a forefinger to nudge small objects or press buttons.
Martha Howe-Douglas as Lady Stephanie 'Fanny' Button – a pompous, overbearing Edwardian lady of the manor and distantly related to Alison. She was pushed out of a window in 1912 by her adulterous husband George, and can be seen in photographs, earning her the nickname "the Grey Lady" (a ghost archetype). She unconsciously re-enacts her death every night at 3:00 am until Julian alters a clock so that she does it a few hours later, making her scream serve as a morning alarm.
Jim Howick as Patrick 'Pat' Butcher – a friendly, polite leader of a uniformed youth group resembling scouts, who was accidentally shot through the neck with an arrow on the Button House grounds in 1984 by one of the uniformed boys in his care.
Laurence Rickard as 'Robin'/ Rogh – The oldest ghost: a caveman who lived on the land Button House now occupies and was killed when lightning struck the tree he was using to hide from a bear. He can manipulate electricity (likely due to his lightning-themed death) and enjoys playing chess, which he learned from Julian, as well as performing ancient rituals for the moon, which he calls 'Moonah'. He can also be heard by living animals. Despite speaking in broken English, his witnessing thousands of years of human history has made him very wise and level-headed. According to the fourth episode of the second series, all the other main characters are distant descendants of his.
Rickard also appears as the head of Sir Humphrey Bone – a Tudor nobleman who accidentally decapitated himself in 1575 after being mistakenly accused of his French wife Sophie's plot to assassinate Elizabeth I. He struggles with his body (played by Yani Xander) dropping his head and failing to pick him up.
Ben Willbond as 'The Captain' – a stern, closeted gay World War II Army officer, who was stationed at Button House during his service, never saw frontline combat, and had secret romantic feelings for his lieutenant. Still obsessed with his time in the war and his rank as an officer, he fancies himself as the de facto leader of the ghosts and likes to orchestrate plans using military strategy. He died of a heart attack when he attempted to reconnect with his lieutenant after the war by sneaking into a combat veterans' gathering at Button House. In the fifth series, his given first name is revealed as James.
Katy Wix as Mary Guppy (series 1–4) – a Stuart era witch trial victim who was burnt at the stake in 1612 and smoulders when stressed. The living can smell burning if she passes through them. Though Mary is timid and superstitious, she is outspoken in other ways. She has a gentle flirtation with and closeness to Robin, but ascends into the afterlife in the fourth series.