March 1941. Joseph Gunner is back on the streets of Glasgow after being wounded on the front lines in France. Keeping the pain in his leg at bay with the help of morphine, Gunner, a former detective, is hoping to lie low as the Luftwaffe begins bombing Glasgow.

But when he runs into his old boss Drummond, he is persuaded to help examine a body found in the wreckage. When it turns out to be that of a German, mutilated to disguise his identity, Gunner reluctantly agrees to investigate. As he begins to hunt for the truth Gunner runs into old flames and bitter enemies, before finding himself embroiled in a high-level conspiracy that reaches far beyond his hometown of Glasgow.