Hide and Seek (2005)

Robert De Niro plays David Callaway, a psychiatrist whose wife has recently committed suicide.

Distancing himself and his daughter Emily from the scene of the tragedy, they move from the city to a New York State summer home, complete with lake. But it is winter, the other houses are shut and the weather is bleak. Emily, refusing to be comforted, takes refuge in her imaginary friend Charlie. At first, her father indulges her, but blood-stained bathroom walls, drowned pets and veiled threats to his new friend Elizabeth Young lead to murder.

Are Emily and Charlie involved or is there another explanation?