I have to say, these Doctor Who audiobooks are very well done! They are entertaining, well narrated, and easily conjure pictures from the TV episodes as I listen to them, even if I've not seen the entire episode (as was the case with Doctor Who and the Visitation). There were a couple of points...
Nyssa, Tegan, Adric and the Doctor end up in England, 1666 and prevent an alien from spreading plague. I love this batch of Companions--they interact with the easy, prickly intimacy of siblings. And some of them are actually useful in a crisis!