Edward Grove was a sentient Edwardian house, alive only during the moments of the chimes of midnight. It created a two hour time loop and fed on the lives and deaths of the servants of the house. At midnight, the people came to life again, and the loop started again.
When the Eighth Doctor and Charley Pollard went to the house on 25 December 1906, they created a paradox which made the house stronger. When they saved scullery maid Edith Thompson, the paradox and the time loop were broken and Edward Grove was defeated. (AUDIO: The Chimes of Midnight)