The British secret service was the best in the world, in experience, technology & contacts. When America entered the war,they had to share & they didn't like it one bit. They looked with distain & mistrust at the fledgling American intelligence efforts. They obstructed, were in flexible & fought for every inch of turf. The Yanks & the Brits both mistrusted the French. That & lots of names was the first half of the book (audiotape). Frankly a little boring.
The book picks up as Mr. Casey gets a little autobiographical with his actual involvement in 1943. What the Americans brought to the table was economic intelligence such as the cost benefit of strategic vs tactical operations, air vs ground activities etc. This type of intelligence was apparently unknown to the British. Mr. Casey discusses the opposition, even in Germany & the military to Hitler & the Nazis It was considerable. He evaluates the resistance groups in the occupied countries.
The result is an entertaining, informative & inside look at Allied espionage in World War II.