As Ted begins his new career as a professor and is about to meet his future wife, Lily forces Barney and Robin to have "the talk" and define their new relationship.
When Robin fears that Barney is cheating on her, she soon discovers that he is spending his evenings with Ted learning everything there is to know on how to date her
When Lily and Marshall realize that Robin and Barney are the perfect double-date friends, they try too hard to impress and come on too strong. Meanwhile, Ted gets a new nickname from Barney after an unsuccessful hook-up.
Despite their best efforts to be the perfect couple, Barney's know-it-all attitude gets him in trouble with Robin and they are forced to ask Marshall and Lily for relationship advice.
After Barney and Robin hit a rough patch in their relationship, Lily devises the perfect plan to break them up, calling in help from Robin's famous friend, Alan Thicke.
When Barney hooks up with a woman Lily had been saving for Ted, she gets revenge by stealing his "playbook," which contains all the moves he uses to pick up women. But will Barney have the last laugh?
Maggie a girl next door Ted has wanted to date for years has suddenly broken up with her latest boyfriend, giving him and many other guys a chance to score with her.
When Marshall finds out he's the "reacher" in his relationship with Lily and not the "settler," he considers pursuing a sexy and cool female coworker. Meanwhile, Ted finds out Robin is a drinking game for his architecture students.
When Barney is about to complete the perfect week - landing seven different girls in seven days - the gang roots him on in order to forget about their own miserable week.
Barney runs into problems when he displays his cell phone number during the Super Bowl, Ted asks Marshall and Lily to arrange a marriage for him, and Robin thinks that her co-anchor has asked her out on a date.
When the gang tries to convince Ted that he is being strung along by Tiffany, they reflect about relationships where each of them has been in the same situation.
After the guys discover that Robin deliberately got Barney hooked up with an incompatible female writer, they find out that that they didn't realize that Robin hasn't been handling their breakup very well.
Ted angers Lily when he brings a random date to her birthday party, so she is forced to remind him of all the other random women he has brought along to important functions, only to discover that they weren't "the one."
Marshall comes up with a number of different outrageous and embarrassing stories to explain how he was mugged in Central Park, but which of his stories is the truth?
Ted reacts to his mom's second wedding by making the capricious decision to buy his "dream house," while everyone tries to figure out whether Barney or Robin cried at the wedding.
As Robin contemplates moving in with her new boyfriend Don, Ted and Barney both decide that they want her back. Meanwhile, Marshall and Lily think they've revolutionized modern marriage when they begin sleeping in separate beds.
Ted is livid when he discovers that the man Stella left Ted for at the altar wrote a blockbuster movie about the incident, and portrays Ted as the bumbling, mean-spirited bad guy.
Marshall and Lily think they've spotted Barney's doppelganger, which means that they can start trying to have a baby, but it's really Barney in disguise. Meanwhile, Ted goes blonde and Robin considers taking an anchor job in Chicago.
