After his capture at Dunkirk, Captain Pat Grant is marched to Laufen Prison Camp in the very heart of the German Reich. Trapped, exhausted, demoralised - a systematic reconnaissance of the prison only proves that escape is impossible. Then Grant finds three six-inch nails...

The Gestapo is puzzled by Lieutenant Richard Player. Is he a British spy? He is sent to Berlin and entrusted to Count von Eissinger, who is determined to establish the truth.