Probably my favourite Gatiss episode. As much as I often find Murray Gold's music sentimental and intrusive, I think he works really hard in this one. I think maybe what I like about it is the structure: certainly the pre-credits sequence is fantastic, and the flashbacks liven up what could otherwise have been a fairly straightforward story. Also, for fans of Emma Peel, it's always a delight to see the wonderful Diana Rigg. Even now, I still can't quite believe she agreed to do it.