Barney uses Lily to get rid of his one-night stand that won't go away; newly-single Marshall realises how couple-orientated the world is.
A blast from the past rocks Callen and Sam when a presumed-dead acquaintance reaches out to them for help. So begins a complicated investigation centred on a potential breach of America's economic sanctions against Russia.
Just when Derek's condition seems to be improving, a severe complication arises; when Cain's former girlfriend is admitted to the hospital for surgery, the doctors finally get a glimpse into his personal life.
House and the team try to diagnose a man's severe, chronic pain; Thirteen and Foreman explore their complicated relationship; Cuddy discovers that caring for her baby leaves her with little time to run the hospital.
The students rally together to find a creative way to stop the school from cutting art and music when their creative departments are under threat from being shut down from the school board.