This really is an excellent book and a true story to boot. It is about a senior member of the KGB, during the cold war, who was unhappy about what the Soviet Union was doing in terms of the restrictions being placed on individuals. The big catalyst was the building of the Berlin wall. He eventually defected to Britain and was instrumental in greatly assisting the British and indeed to the West's approach to the Soviet Union which may have prevented a further escalation of tensions. The book has many tense moments, not the least of which was the exfiltration of said spy when he had been rumbled by the Soviet authorities via Finland.