Drama series presenting a portrait of an upper-class family enduring passion and loss in World War Two Britain. The three Cazalet brothers struggle to cope with thwarted ambitions, adultery and battle scars, while the youngest daughter hides a shocking secret.

It is summer 1939; war is imminent and is officially declared in September. Philandering Edward arrives home with his glamorous mistress, while Villy is shocked to discover she's pregnant and takes drastic action. Meanwhile, Zoe returns to London to nurse her sick mother and strikes up a relationship with a doctor.

Zoe discovers she is pregnant by Rupert, who joins the Navy and goes missing in the Dunkirk evacuation. Meanwhile, Sybil falls seriously ill but suffers in silence, and Edward's long-term affair with Diana continues.

A distraught Clary pursues her father through France, leaving Zoe to cope with the newborn baby, and Sybil continues to hide her illness from those around her : despite undergoing major surgery. Meanwhile, the business suffers as the Blitz intensify, but Louise is distracted by a chance meeting with a dashing older man.

Troubled Neville fears the worst about his father's disappearance and flees the family home, while Zoe gets involved with one of her patients and Louise confronts her father about his illicit affair. Sybil's health deteriorates and Christopher speaks out against the horrors of war : only to be consigned to a psychiatric hospital.