The supposed twist (and consequently, the last third or so of the story) is unutterably clichéd, but this is still a really fun story. It's not as Underground-heavy as, say, The Web of Fear, but it does manage to get in some jibes at Crossrail. I always like DW incorporating mythology and folklore, so I liked the use of elves, and the details like the king feeding birds from his 51st-floor penthouse. Great dialogue too.