While I’m not planning to go into a lot of plot details, it’s likely that the random mutterings that follow will reveal some things you might prefer not to know if you haven’t seen the episode yet, so in my usual way, I’ll include this warning:
Yes, I’m a bit late with this one, but never mind, here goes. After getting upset with the Doctor’s disinclination to decide what everyone should do about the moon, Clara has agreed to one last fun trip with the grumpy Time Lord. A trip on the Orient Express! Well, more a trip on an Orient Express, really. Rather in the manner of the Titanic in Voyage of the Damned, this is the Orient Express in space, with everyone in suitable costume and people dropping dead all over the place, leaving the Doctor to play Poirot. The people who are dropping dead seem to be seeing yer actual traditional shambling Egyptian mummy, complete with nice bits of decay, a dragging foot and not actually being visible to anyone except its latest victim. Which is a bit different from the usual mummy trick, and it takes a trick from the Doctor for him to see it and utter the immortal words
Are you my mummy?
before working it all out in just enough time not to be killed himself. Much fun is had by all, even Clara, once she gets over being slightly trapped for much of the episode. So much so, that she decides that maybe this won’t be her last trip with the Doctor after all. Which I’m sure surprised everyone. Or not.
Frank Skinner had a nice guest role as the engineer who quite sensibly declines the offer to travel with the Doctor.
Some more of the usual behind the scenes stuff in the latest Doctor Who Extra:
 I don’t need to explain that one, do I?