Ted is nervous about his first lecture as a college professor. He can’t choose between being cool or being authoritative. He ends up in the wrong lecture hall and makes a fool of himself. Meanwhile Lily discovers that Barney and Robin have been hooking up all summer. She demands that they define their relationship but they refuse. So she locks them in Robin’s bedroom and forces them to have “the talk.”
Ted goes on a blind date and realises he went out with the same woman seven years before. Barney takes Marshall to a strip club where they find a stripper who looks just like Lily.
Barney is finding it hard to be a boyfriend. Ted offers to teach him Robin 101 and he reluctantly agrees. Ted uses his college classroom to impart all of his knowledge about Robin. Robin and Lily find Barney's notes and get angry. They confront Ted and Barney who both apologise. Robin forgives them and realises that Barney was doing his best to be a good boyfriend. Meanwhile Marshall tries to get rid of an old barrel but no one wants it.
Ted tries to prove that tweed will turn women on. Marshall and Lily try really hard to make Robin and Barney their new best couple friends. Robin and Barney “dump” them for being weird but soon regret it. When Marshall and Lily make friends with a new couple Barney and Robin realise what they are missing.
Robin gets into a bar fight and faces deportation. Barney helps her prepare for an American citizenship test but she begins to question her identity. Ted and Marshall learn that their favourite road trip destination is closing and they decide to drive there one last time. But Marshall brings Lily much to Ted’s disappointment.
The couple who live above Ted are making love so loud that it is disturbing him. Barney claims that he and Robin never fight but Ted suspects they are lying. Barney advises Marshall to confront Lily over washing dishes. Marshall does and it leads to a huge fight.
Barney gives Ted his porn collection and on one of the videos is a hidden message asking Ted to save him from a committed relationship. Soon Barney has developed a ‘relationship gut’ and Robin is letting herself go. The two seem increasingly unhappy but too stubborn to break up. Lily eventually agrees to help Marshall and Ted break them up.
With their break up fresh Robin and Barney take different approaches to moving on. She throws herself into work which leads Ted and Marshall to point out that it’s moments like this that people find love. Barney throws himself back into dating or to be more specific conning women into bed. He uses “The Play Book” his own collection of scams and manages to incorporate Lily into his schemes.
Its thanksgiving and Marshall bequeaths his fourth Barney slap to Robin and Ted. They can’t decide who should slap him. Lily’s Dad arrives for dinner but she doesn’t want to see him.
Ted gets a call to tell him that “the window is open” meaning Maggie Wilkes has broken up with her boyfriend. Maggie is the ultimate girl next door type who men are drawn to. Each time she has broken up with a boyfriend she has gotten a new one before Ted can get to her. When he realises he has to teach a class that night he leaves her with his friends to ward off other men. Meanwhile Marshall’s mother keeps sending him boxes of his old stuff which she wants to get rid of. His old overalls find a new home when Barney takes up the challenge to get laid while wearing them. Then a letter from his fifteen year old self makes Marshall sad.
Older Ted reveals to his children that the group used to smoke. Robin in particular was a consistent smoker. She is upset that her new co-host Don is deeply cynical and unprofessional. Marshall ends up smoking again as a way to bond with his new boss and his former boss, Arthur Hobbs. Lily, Ted and Barney all get sucked in and try to help each other quit for good.
A hot bartender (Stacy Keibler) starts work at McLaren’s and Barney is determined to seduce her. The only problem is she hates suits. Meanwhile Ted dates a college student whose roommate is his future wife (the mother).
Marshall tells stories about a hilarious new coworker called Jenkins. But he feels guilty because he allowed Lily to believe it was a man when it’s actually an attractive woman. When Lily finds out, she isn’t jealous at all and Ted thinks it’s because Lily is the “settler” and Marshall is the “reacher” in their relationship. Marshall wants to prove her wrong and when Jenkins kisses him Lily gets mad. Meanwhile Ted’s students all watch Robin’s show but only for a drinking game.
Barney is waiting to learn if he still has a job. As he waits he imagines himself being interviewed by Jim Nantz. He recounts the story of the past seven days where he has slept with a different woman every night. Meanwhile his friends are all discussing their own problems each day. Ted embarrassed a student by making fun of her name, Robin had a bad date but the guy doesn’t call her back and Lily and Marshall lose out on a new friendship because they share a toothbrush.
Barney holds up his cell phone number during the Super Bowl and it won’t stop ringing. He loves the possibilities but it starts to make him go crazy. Ted gets tired of searching for women and asks Marshall and Lily to arrange his marriage. Robin agrees to go out with Don on Valentines Day and denies that she has feelings for him.
Ted thinks he is about to score with Tiffany (Carrie Underwood) until she tells him she has a boyfriend. Ted’s friends explain how she is keeping him on the hook. We soon learn that Ted, Robin and Lily (with ex-boyfriend Scooter) are all guilty of the same thing. Barney is excited to learn that Tiffany is a pharmacology sales rep because that is the current “hot girl profession.”
