In all the furore over the past week about the commencing of shooting for the fifth season of the revived Doctor Who, it was almost pushed to the side that there are still three special episodes due to air this year, that will see David Tennant pass the torch and Tardis keys over to Matt Smith.

The first of these will be arriving on our screens in November, and it's The Waters Of Mars, a new trailer for which was premiered at Comic-Con in the States. There's potential for The Waters Of Mars to be a really nice episode, and I'm liking the idea of, once again, taking something regular and everyday - in this case, water - and turning it into something a bit more sinister. In the midst of the global swine flu panic, the story may also end up having a bit more resonance than originally thought on the basis of the trailer.

We also get someone knocking four times, as foretold in Planet Of The Dead earlier this year. Who's doing the knocking? Are we going to find out in The Waters Of Mars? It's hard to be sure, but this new trailer, nonetheless, is a good, solid reminder that Mr Tennant's days are far from numbered right now...

Catch the round-up of the Doctor Who Comic-Con panel right here.