Edward Grove was a sentient Edwardian house, alive only during the moments of the chimes of midnight. When the Eighth Doctor and Charley Pollard went to the house on 25 December 1906, they created a paradox which made the house stronger. Typically such moments of sentience were temporary events caused by traumatic events, such as a murder, but the presence of the Doctor and Charley unintentionally created a temporal paradox. Scullery maid Edith Thompson would go on to work for the Pollard family in the 1930s, but she would commit suicide after Charley's apparent death in the R-101 crash, only for Charley's appearance in 1906 to essentially remove Edith's reason for killing herself.
As a result, Edith Thompson's death became a focus of a two hour time loop 'inhabited' by the residents of the house, each of them trapped in a loop where some of them would die at the moment that the clock struck. At midnight, the people came to life again, and the loop started again.