Most importantly, he finds that Williams was compelled to turn Doctor Who into the Tom Baker Show, which is of course great for us Tom Baker fans, but not so great for the show's long-term health. Nathan-Turner then took over and found himself in the same position as Innes Lloyd in 1966 - the show was defined around the lead actor; how to take it forward without him? One senses that Sandifer has more to say about JNT in future volumes, but here he concentrates on Christopher Bidmead's contribution to Season 18. There are the usual excellent side essays - one previously unpublished on versions of Shada, several on comics, novels and other SF media (in particular Star Wars), an explanatory note on the Winter of Discontent, and what I think is the first write-up of a Big Finish play in this series of books (a lovely piece on The Auntie Matter).
I confess I was a little disappointed on one or two points. The pieces on The Invasion of Time and The Leisure Hive didn't actually say much about either story, and I think both are interesting in their own right, for good or ill. Although he rightly singles out Lalla Ward for praise, I would have liked to read more about Louise Jameson and particularly John Leeson, who is given less page time than Matthew Waterhouse. A sequence of thought about David Fisher is started but not finished. There seems to be a lot of dialogue with Wood and Miles. And some of the key points about Williams and Nathan-Turner, summarised above, are repeated as often as you would expect in a series of blog posts, but perhaps more often than you would expect in a book that has been edited.
Still, if this is the weakest of the four volumes so far, that should in no way be considered faint praise; I'm nominating it enthusiastically for the BSFA and Hugo awards next year, and I hope you will too.