On balance, I would put this between a 3 and a 4, but I gave it a four for coherence. Still, this author is not John Le Carre at his best (George Smiley series).
What I found most interesting, as I read through the book and found connections with both my past and with Japan, was the manner in which the author appears to have found a formula for connecting what he has done in his own past, what he has read about, and what he is presumably writing off on his taxes–comprehensive travel.
I put the book down, not disappointed–I certainly recommend this book to anyone who has not been a spy–but thinking to myself, WOW, this is what I can do when I retire–travel all over the world, write a spy novel with details about each place I visit, and presto, it is all a grand tax write-off.
Professionally speaking the book is way too facile. Planting an audio device is very very tough. The need for line of sight from the transmitter to the receiver kills most applications. Generally speaking, you have to listen for four hours to get five minutes worth of useful stuff. Killer technologies certainly abound, but as CIA found when it tried to kill Castro with exploding cigars, infected dive suits, beard killers, and the bomb-dropping pigeons, generally technology is not the answer.
3 for former spies, 5 for the general public, 4 on balance. Absolutely recommended for a rainy afternoon.