Downton Abbey--a sprawling Edwardian mansion and park nestled in the lush North Yorkshire countryside--needs an heir. A tragedy at sea has claimed the life of the presumed heir, and Lord Grantham is faced with the possibility that the house he's loved his whole life might one day belong to a distant cousin he's never met. Before he can worry about that, he must deal with his scandalous daughter, Lady Mary, who many believe to be the rightful heir...

The Great War rages across Europe, and not even the serene Yorkshire countryside is free from its effects. The men and women of Downton are doing their part: heir Matthew Crawley and footman Thomas Barrow are off fighting, while Lady Grantham and Isobel Crawley are squabbling over whether Downton should be used as a hospital. Lady Mary is seeing a wealthy newspaper magnate while Lady Edith becomes much warmer and Lady Sybil seeks to ingratiate herself...

During an impromptu trip to Europe to mend a broken heart, Frank unexpectedly finds himself in a flirtatious encounter with Elise, an extraordinary woman who deliberately crosses his path. Against the breathtaking backdrop of Paris and Venice, their whirlwind romance quickly evolves as they find themselves unwittingly thrust into a deadly game of cat and mouse.