Mary is struggling to come to term with Matthew's untimely death. Downstairs, hearts are broken as Jimmy finally takes an interest in Ivy. And Thomas is up to his old tricks and has the children's Nanny in his sights.

The Crawleys head for the Scottish highlands to enjoy the hospitality of Rose's family while most of the staff stay behind. New crisis unfolds amid the stay, and Mary finds herself in need to return to Downton early.

Emerging from her grief, Mary starts to take an interest in the running of the estate but is met with resistance from Robert. Bates hatches a plan to help Molesley, and Rose gets into a sticky situation at a tea dance in York.

An extravagant house party at the Abbey gives the Crawleys a chance to reconnect with old friends. Some guests, however, prove more welcome than others and along with the celebrations come skulduggery and heartache.

Amid the fallout of the eventful house party Mary faces a pressing question about her future, Carson reveals surprisingly intimate details of his former life, and a trip to London sees Rose put the reputation of the Crawleys in jeopardy.