If you get the Nevil Shute bug you are infected forever. This book is not his best, suffering a little from the disjointed nature of the plot and the long starting section giving you the backstories of each of the characters. Yet it is a credit to Mr Shute that multiple backstories and a very "boys' own" storyline of wartime heroics can be gripping more than 50 years later.
"Most Secret" refers to the classification of reports concerning a fishing vessel and its secret missions to wartime France. The book describes the creation of a disparate crew of experts to carry out raids on occupied Brittany. While as ever Nevil Shute is extremely readable, the storyline lacks the flow and panache of say, A Town Like Alice or Pied Piper. This is the fault of the plot to a certain extent - the "Most Secret" dispatches forming focus points around which the plot is revealed curtail the flow. The other slight problem is that there is no one character with which to sympathise - by creating several leads the reader struggles to know who to focus on.
Notwithstanding these criticisms, I would still recommend this book. For a Nevil Shute fan it's a must, but it's unlikely to convert too many new fans. I still read it in a couple of days though, and now I want to re-read all my other Nevil Shutes - his writing has that kind of effect on you.