Freemantle puts himself through an exceptional exercise - delivering a set of connected short stories, each a full espionage thriller in miniature, tied together by characters from a single English intelligence bureau, and, from the beginning, concerned with who the Soviet mole in it is.  It suffers a little from the answer being so obvious that when a last-minute misdirect occurs, we are more annoyed than tricked, but ultimately it's better than an actual twist ending. Much better. The many personalities, and moreover, technical specialties of the operatives, are on full display, and you are always eager to see what the next star will bring to the table.  Freemantle wants you to love the men and women of the Factory and worry for their safety, via the traitor, and by spreading the spotlight around even to people like the financial analyst and the old-timey puzzle guy, accomplishes it masterfully.