I've read Ben Macintyre's Operation Mincemeat: How a Dead Man and a Bizarre Plan Fooled the Nazis and Assured an Allied Victory and Agent Zigzag: A True Story of Nazi Espionage, Love, and Betrayal and his last book Double Cross: The True Story of the D-Day Spies about MI5 work in WW2 is just interesting and well written as the two previous books.
In this book Macintyre focuses on the work of five double spies: Dusan "Dusko" Popov, Roman Czerniawski, Lily Sergeyev, Juan Pujol Garcia and Elvira de la Fuente Chaudoir, their handlers (both German and British) and MI5 and Abwehr staff.
Macintyre tells of many various interesting characters and fates but I found myself most interested in Johann "Johnny" Jebsen. Jebsen was German intelligence officer and British double agent who was betrayed by a "friend".
This book is a real page turner and truly " real life is more incredible than any fiction".