Rebecca Faulkner, codenamed Butterfly, is a deep cover US intelligence operative who is set up for a murder that she didn’t commit. Caught in a deadly global manhunt, and disavowed by her own handlers, her attempts to get home from foreign soil unwittingly lead her to a man she thought died twenty years ago — her own father, David Faulkner, a former Cold War spy codenamed Nightingale, now living under an assumed identity and with a new family. Father and daughter, two spies spanning two very different eras, have to pool their resources and trust each other through decades of hurt, secrets and lies to unravel the conspiracy behind her predicament: a conspiracy which may have its roots in his sinister past.