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.

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.

Concern grows over Sybil's condition, while Christopher convalesces at Home Place. Two-timing Edward discovers that Diana is pregnant, Michael gets down on one knee to a confused Louise and an unexpected visitor brings welcome news of Rupert.