Ricky Tarr was a field agent with the Secret Intelligence Service before he went missing in Hong Kong, presumably to defect to the Soviet Union. Months later, Tarr has reappeared, bringing with him a story so damaging that almost no-one can be trusted to hear it. His old mentor, retired spy chief George Smiley, must follow a thread of treachery into the heart of the British establishment, suspecting friends and former colleagues at every step.