If you have seen the latest Doctor Who you'll know what this posts title means.

A very creepy ending for Planet of The Dead, The Doctor gets a warning that something is coming back, that someone will knock four times, and that his song is ending. Could this be the return of his old enemy you see die at the end of season 3? The Return of The Master? and the return of Donna Noble? We'll see in the next Doctor Who special : The Waters of Mars.