In 1942 code-breaker Claire Hopkins is the victim of an unsolved murder. Fourteen years late her former colleagues Millie and Jean read of two murders in San Francisco identical to Claire's and the pair travel to the city to meet war-time counterparts Iris Bearden and Hailey Yarner. Iris's son Dennis, a civil rights activist, is part of a group opposing property developers bull-dozing their district, Fillmore, for gentrification. After a third murder the women find a possible clue to the killer in a letter to the local paper.

Subsequent deaths make it clear: San Francisco is in the grip of a killer with a dark and complex agenda now menacing Iris' own neighborhood. The four unlikely allies struggle to work together - and in the process, not only expose a twisted operation, but also forge powerful and lasting bonds.

Our four women delve into the mysterious death of Iris' suburban friend, uncovering a complex cluster of marriages built on lies and deception. In her quest to forge a new life, Millie must confront a long-lost cousin, who may hold the key to a future in San Francisco.

After a seemingly innocent man is charged with murder, the women become enmeshed in a tangled suburban tragedy, racing to find both the true killer and the methods before the scent goes cold. Jean meanwhile grapples with how -and where - to build a new life for herself.

A bloodied and battered stranger collapses on Millie and Jean's doorstep, dragging them into a mysterious criminal underworld. In a race against time, the four women must unravel the patterns behind a series of attacks in order to avoid becoming the next victims.

Having uncovered a covert system of police corruption, the women must go it alone, crafting a complex sting operation in order to draw out two warring factions and see justice done. Time is precious, as their investigations have triggered deportation proceedings that could soon send Jean and Millie back to the UK.

When a Russian diplomat dies in Iris's arms, the FBI sweep in to control the story and rule the death accidental. Iris is forced to get involved to protect her family. Hailey meanwhile befriends a world-renowned visiting cellist, and all four soon find themselves embroiled in a dangerous international firestorm.

A death in the Big Bop Club brings an international incident right to their doorstep, while the women grapple with Jean's sudden disappearance. Reeling from betrayals, Iris and Hailey work with Millie to plan a daring undercover operation to find Jean and expose Cold War treachery.