DOWNTON Abbey star Michelle Dockery is to join Rufus Sewell and Michael Gambon in a BBC adaptation of best-selling novel Restless.
The two-part film - based on the book by William Boyd - will also star Hayley Atwell and Charlotte Rampling playing the same character more than 30 years apart.
Acclaimed theatre director Edward Hall is to dramatise the tale about a female spy on the run who has led a double life for three decades.
Dockery plays a young woman, Ruth Gilmartin, who learns that her mother Sally (Rampling) was recruited by the British Secret Service at the start of the Second World War, but has been in hiding since a mission went awry.
Atwell - who plays the younger Sally - has previously starred in a Channel 4 adaptation of Boyd's Any Human Heart.
Boyd said: "To have the chance to film a novel like Restless over three hours is the sort of opportunity that only a television adaptation can provide.
"It represents the most enticing and alluring of possibilities - not only to tell an enthralling story of wartime espionage, love and betrayal but also to lift the lid on one of the last secrets of the Second World War."
It begins filming in South Africa and the UK this summer and will be screened later this year.