Wartime codebreakers Millie and Jean travel to San Francisco to hunt a serial killer who resurfaces 14 years after the murder of their dear friend.
As a menacing murderer grips Iris’ suburban neighborhood, tensions surface between the four women as they struggle to untangle a growing conspiracy.
The accidental discovery of another victim reveals a nest of marital lies and deception that lead Millie, Jean, Iris and Hailey to a useful codebook.
Detective Bryce makes an arrest while the women continue to pursue the real killer. Meanwhile, Jean tries to build a new life in San Francisco.
An unsettling encounter with a bloodied stranger drags Millie and Jean into a violent criminal underworld, in which a surprising person is involved.
When the clan unearths a corrupt police operation involving mysterious attacks, Millie and Jean gain new enemies and face deportation back to the UK.
When Iris witnesses the death of a Russian diplomat, the women gain unwelcome attention from the FBI and KGB. Jean enlists help from an old friend.
Now deeply embroiled in a KGB cover-up, one of the women is suddenly captured and the others must plot a daring operation to rescue her.