Her brow furrows at his answer, uncomprehending for a moment. 'My letter?' And then she remembers; a letter written in impulse, out of anger at the Doctor and sorrow for what she'd thought was a friendship at its end, left in some hotel for him. 'Oh my god, my letter, I'd entirely forgotten. I never got to tell you,' she murmurs, the realisation dawning, 'And then you went back to Singapore... Oh, I was an idiot.'