This terrific book is the fascinating true story of a secret British organisation created at the outbreak of WWII with the express intention of disrupting Hitler's war machine through acts of sabotage and guerilla warfare. Although backed by Winston Churchill, the proposed activities of the group (whose nickname gives this book its name) were seen as very much against the "values" of the British army and had to prove their worth through staggering acts of invention and courage (including the improbable mission to assassinate Reinhard Heydrich, profiled in Laurence Binet's brilliantly inventive novel HHhH).
What Giles Milton does brilliantly in this book is focus on a set of (very individual) real characters as a way into the story, allowing a compelling (and dare I say, novelistic) perspective to this already over-analysed segment of history. History buffs will appreciate the fresh research and insight, and those only lightly-versed in WWII literature will be riveted to the page by these tales of derring-do and invention.
If this sounds like your cup of tea, I would also recommend some other character-driven narrative histories of WWII: Nicholas Rankin's Churchill's Wizards, Norman Ohler's Blitzed and Antony Beevor's The Second World War.