Millie and Jean go to San Francisco to work with American codebreakers Iris Bearden and Hailey Yarner to chase a serial killer from their war days.

When a killer is is menacing Iris' neighbourhood, the four unlikely allies join forces to stop the murderer. The allies struggle to work together, but expose a twisted operation and forge bonds.

The women investigate the mysterious death of Iris' suburban friend, unearthing a complex cluster of marriages built on deception and lies; Millie needs to confront a long-lost cousin.

The women become enmeshed in a tangled suburban tragedy after a seemingly innocent man is charged with murder; Jean grapples with how to build a new life.

A bloodied stranger collapses on Jean and Millie's doorstep, drawing them into a criminal underworld. The women race against time to investigate a series of attacks before they become the next victims.

The women go it alone after uncovering a covert system of police corruption, planning a complicated sting operation to try and draw out two warring factions and see justice done.