Great book for understanding sengoku era shinobi usage in general and Takeda Shingen's way in particular.
There's a lot of misinformation going around about this subject, and the best way for finding out true and false is to be guided through authentic early materials by an expert such as Serge Mol with his impressive research done in this book.
In this book you'll get the broad perspective of a war lord establishing a shinobi network, and a particular look of shinobi at his very versatile field work in both peace and war time.
Why did Shingen establish his own shinobi network insted of using Iga and Koka no mono? Why were horse doctors valuable agents? How would a shinobi deal with guards? and with counter espionage? how would he manage out in nature? what were his patrol strategies in his own battle camp? and why would he use a placenta???
You'll get the answers in the book along with many historical anecdotes which bring the text into life.