Excerpt from A Spy Among Friends by Ben Macintyre, plus links to reviews, author biography & more

In the spring of 1941 the body of a Dutchman was found in an air-raid shelter in Cambridge. His name, unimprovably, was Engelbertus Fukken. In his pockets and suitcase were found a Dutch passport, a forged identity card, and one shilling and sixpence. He had parachuted into Buckinghamshire five months earlier, passed himself off as a refugee, and shot himself in the head when he ran out of money. No Nazi spy had managed to remain at large for so long, and there was no trace of him in the Bletchley Park intercepts, which raised, for Elliott, the worrying possibility that there might be others at large.

Under Cowgill's relaxed regime, the officers of Section V could visit London "virtually at will." Philby and Elliott seized every opportunity to do so, in order to cultivate "contacts with other SIS sections, with MI5 and with other government departments" while also visiting their clubs and, in the summer, watching cricket together at Lord's. Both volunteered for "fire-watching nights" once or twice a month at MI6 headquarters, monitoring the telegrams that came in overnight from around the world, which offered a fascinating insight into British intelligence operations. Among the secret brethren, Elliott and Philby were the closest of siblings, reveling in the shared risks, hard work, and ribaldry.

One morning in 1941, Kim Philby caught the train to London, taking with him, as usual, a "bulging briefcase and a long visiting list." He also carried a detailed description of the workings of Section V and its personnel, aims, operations, failures, and successes, written out in "longhand, in neat, tiny writing." After completing his round of meetings at MI5 and MI6, Philby did not head to the bar beneath MI6, nor to his club, nor to the Harris home for an evening of drinking and secret sharing. Instead he descended into the St James's Park Underground station. He let the first train leave without boarding. Then he waited until every other passenger had boarded the next train before slipping on just as the doors closed. Two stops later, he alighted and caught a train in the opposite direction. Then he hopped on a moving bus. Finally certain that he was not being followed ("dry-cleaned," in spy jargon), Philby made his way to a park, where a stocky, fair-haired man was waiting for him on a bench. They shook hands; Philby handed over the contents of his briefcase and then headed to King's Cross to catch the train home to St Albans.

Had Nick Elliott examined the report about Section V written by his best friend, he would have been amazed and then mortified. One passage read: "MR NICHOLAS ELLIOTT. 24, 5ft 9in. Brown hair, prominent lips, black glasses, ugly and rather pig-like to look at. Good brain, good sense of humor. Likes a drink but was recently very ill and now, as a consequence, drinks little. He is in charge of Holland."

Elliott would have been still more astonished to discover that the man hurrying away into the night with the bundle of papers was an officer of the NKVD, Stalin's intelligence agency (the predecessor organization to the KGB), and that his friend Kim Philby was an experienced Soviet spy of eight years' standing, code-named "Sonny."

Excerpted from A Spy Among Friends by Ben Macintyre. Copyright © 2014 by Ben Macintyre. Excerpted by permission of Crown. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.