A leak is traced to a small sub-section of SIS, sparking off the inevitable security checks, tensions and suspicions. The sort of atmosphere, perhaps, where mistakes could be made? For Maurice Castle, it is the end of the line anyway, and time for him to retire to live peacefully with his African wife, Sarah. To the lonely, isolated, neurotic world of the Secret Service, Graham Greene brings his brilliance and perception, laying bare a machine that sometimes overlooks the subtle and secret motivations that impel us.