The Great War is over and the long-awaited engagement of Lady Mary and Matthew is on, but all is not tranquil at Downton Abbey as wrenching social changes, romantic intrigues, and personal crises grip the majestic English country estate. Shirley MacLaine joins the much-loved cast, which includes Dame Maggie Smith, Elizabeth McGovern, Hugh Bonneville, Dan Stevens, Michelle Dockery, Jim Carter, Penelope Wilton and many others. "No family is ever what it seems from the outside," observes Smith's shrewd character. The fate of Downton Abbey hinges on a letter from a dead man. Edith and Sir Anthony face their own fateful moment. Mrs. Hughes confronts a crisis.