In Waters of Mars, the Doctor claims to have worked out what the four knocks riddle:
No, ‘cos someone told me just recently, they said I was going to die. They said “he will knock four times”. And I think I know what that means, and it doesn’t mean right here, right now, ‘cos I don’t hear anyone knocking, do you? (YouTube clip)
But I can’t work out what he’s referring to. A few ideas that I dismissed:
- He’s guessed correctly. But he seems pretty surprised by it when it happens, and it doesn’t seem like something he’d be able to predict.
- The Master is knocking. But at this point the Tenth Doctor still believes the Master to be dead; he doesn’t learn that he’s still alive until The End of Time.
So do we ever find out what he was referring to here?