Finch and Reese try to protect a psychologist who uses unorthodox methods to help patients achieve closure; flashbacks reveal Finch's state of mind after the death of his best friend.
In the summer of 1923, Rose is presented at Buckingham Palace and has her coming out ball at Grantham House.
An extravagant house party at the Abbey gives the Crawleys a chance to reconnect with old friends, but some guests prove more welcome than others, and along with the celebrations come deceit and heartache.
Amid the fallout from the eventful house party, Mary faces a pressing question about her future, while Carson reveals surprisingly intimate details of his former life.