When an MI5 case file appears without explanation on the eve of the Monochrome Inquiry’s shuttering, civil servants Griselda and Malcolm are drawn into the buried history of a classified operation in Cold War Berlin, which ended in tragedy and scandal—and whose cover-up has rewritten 30 years of Service history.

Agreeing to investigate a cold-case file, private investigator Robert Brixton finds himself in the underworld of Savannah's power elite and uncovers a secret government organization of contract killers who perform "patriotic" assassinations.