Doctor Who: Patient Zero

The first of a trilogy of stories that conclude Charley's story arc with the Sixth Doctor, this begins with the Doctor once again being thwarted in his attempts to find out who she really is. In this case, though, it's not some incidental event that scupper his plans, but a direct threat to Charley herself.

This leads him to a remote space station which, naturally enough, soon comes under siege. And while they are, unusually, not in the title, it's obvious who by from looking at the cover. Nudging this up from a typical base-under-siege story, however, we have the strange nature of the inhabitants (who also make a good use of a limited cast), and the threat that something else equally scary is also on its way. A number of threads from previous stories come together here, and not just those concerning Charley's back story.

Indeed, it's the plotline involving Charley that really makes this shine, as she becomes increasingly imperilled by the titular Patient Zero that everyone else seems so desperate to get hold of. The unexpected cliffhanger ending of story works on multiple levels, making this a story that's anything but standalone.