An Officer and a Spy by Robert Harris

Paris, 1895: an army officer, Georges Picquart, watches a convicted spy, Alfred Dreyfus, being publicly humiliated in front of a baying crowd. Dreyfus is exiled for life to Devil's Island; Picquart is promoted to run the intelligence unit that tracked him down. But when Picquart discovers that secrets are still being handed over to the Germans, he is drawn into a dangerous labyrinth of deceit and corruption that threatens not just his honour but his life...

Eye of the Needle by Ken Follett

His weapon is the stiletto, his codename: The Needle.

He is Hitler's prize undercover agent - a cold and professional killer.

It is 1944 and weeks before D-Day. The Allies are disguising their invasion plans with a phoney armada of ships and planes. Their plan would be ruined if an enemy agent found out... and then The Needle does just that. Hunted by MI5, he leads a murderous trail across Britain to a waiting U-Boat. But he hasn't planned for a storm-battered island, and the remarkable young woman who lives there . . .