The story of this season still revolves around Ted and other five people. Time flows to 2009. Matthew (Jason Segel) and Lily (Alyson Hannigan), who have been in love for many years, moved into a new apartment after getting married and lived a happy and sweet life. Their best friend Ted (Josh Radnor) decided to give up being an architect and switch to being a university professor after repeatedly hitting a wall in the last season. At the same time, he is also trying to find his true love daughter. On the other hand, their mutual friends Barney (Neil Patrick Harris) and Robin (Cobie Smulders) finally got together after a year of emotional struggles and struggles. Lily is very happy about this, but Barney and Robin find it difficult to determine the relationship between each other. With the help of three friends, can they determine the relationship between boyfriend and girlfriend?