The producer and script editor from the third doctor's era reunite to tell us a story. First of a strange encounter that the brigadier had many years ago. And then how the doctor and UNIT get into one of their usual situations. Which ties in with the story of the brigadier's past.
The first part of the book, the brigadier's story, is written by barry letts, who was the producer of the pertwee time. Not having done as many books as terrance dicks, his style is a little less familiar. It's readable stuff that tells a reasonably interesting story, although it has little resolution as a result of needing to tie into what follows.
In the next part, terrance dicks, script editor of the time and author of many novelisations of doctor who stories, brings us a typical UNIT tale. After his last book [warmonger] turned out to be very disappointing, this is a bit of a return to form. It's not the best thing he's ever written, but it's a readable if predictable third doctor story.
And that's what I expected this book to be. If that's what you want from it, you won't be disappointed