As the threat of war looms over Europe in 1938, tensions simmer below the surface of the Cazalet family.

Villy gets pregnant and meets her husband's mistress, while a heart attack has romantic repercussions for Zoe.

As the Second World War is declared, Zoe gets pregnant and Rupert joins the navy. Meanwhile, Sybil is becoming seriously ill, but Edward's affair shows no signs of ending.