Carmen (Planet of the Dead)
From Tardis Wiki, the free Doctor Who reference
Carmen was a middle aged woman, married to Lou, who was onboard the London bus number 200 with the Doctor and Lady Christina de Souza.
She had psyhic powers. She is able to hear the voices of the dead on the planet. When the Doctor saves her, Carmen tells him "Your song is ending, it is returning through the dark, and ... over there he will knock four times."(DW: Planet of the Dead)
