After sharing a kiss at the beginning of the summer, Robin and Barney are unsure how to handle their mutual attraction. After some consideration they tell the gang they have decided to remain just friends, but secretly continue seeing each other. They are able to get away with their secret romance for a couple months, but are discovered when Ted, Marshall and Lily walk in on them together. They explain to the gang that they are happy with their casual relationship, and didn’t want to complicate it by defining it. This is unacceptable to Lily, who pressures them to label their situation, and ultimately locks them in Robin’s room to force them to address it. Meanwhile, Ted is anxious about his first days as a professor at Columbia, which is made worse when he shows up at the wrong class and starts his lecture.

Barney takes Marshall, and Robin to a strip club where they find a stripper who looks almost exactly like Lily. Meanwhile, Ted discovers he had been fixed up with the same woman, Jen seven years earlier.

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.

Marshall and Lily want to hook up with Barney and Robin for double-dating and fun, but their desperate eagerness to please is a huge turn-off. Meanwhile, when a succession of girls come to his apartment and immediately fall asleep, Ted is bummed to learn he is a "Sexless Innkeeper" whose "dates" are only interested in a comfy place to crash

Barney tries his best hoping to convince Robin into becoming an American citizen, while Ted and Marshall's road trip takes an unexpected turn for the worst when Marshall invites Lily to come along.

Even though they do their best in order to be the perfect couple, Barney's attitude of know-it-all lands him in trouble with Robin and they are forced to seek Marshall and Lily for advice.

Lily comes up with a perfect plan to break up the relationship between Barney and Robin when they have a rough patch, but she needs help from Robin's famous friend, Alan Thicke, in order to make it work.

After his relationship with Robin ends, Barney dusts off his "playbook" to help him back into the dating scene

Barney freaks out when Marshall bequeaths a "slap bet" slap to Ted and Robin. Meanwhile, Lily's estranged father shows up for Thanksgiving.

When a perfect girl finally shows up, the gang tries everything to help Ted, while Marshall takes action when he discovers a letter written by younger himself.

When Marshall picks up smoking again, it prompts Lily, Ted and Barney, ex-smokers all, to succumb as well. Meanwhile, Robin gets a new co-anchor at her show...

When Barney debates giving up wearing suits in order to land a hot bartender, his conflicted feelings lead to an amazingly awesome musical number. Meanwhile, Ted gets one step closer to meeting the future mother of his kids.

When Lily refuses to believe that Jenkins, Marshall's attractive female colleague, kissed him, Marshall insists Jenkins tell Lily what really happened. Meanwhile, Robin finds out that a drinking game has been made up about her.

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.

When Lily and Marshall forget to fix up Ted on a blind date for Valentine's Day, they use one of Barney's many discarded girls to see if they may become Ted's future wife. Meanwhile, Robin's obnoxious colleague invites her to a party at his apartment

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.

When Robin confesses that she is still angry with Barney for the way he handled their break-up, she enlists the help of Anita, a self-help author who plans to beat Barney at his own game.

When Ted ruins Lily's birthday dinner celebration by bringing a date, Lily goes to great lengths to keep her out of the traditional photo she takes every year of the gang.

When Marshall gets mugged, Lily decides she wants to get a gun for protection, so Marshall comes up with a convoluted story about the mugging to deter Lily from following through.

When Ted attends his mother's wedding, he is extremely disturbed by her overly affectionate relationship with her fiancé, which forces him to think about his own life and make an impulsive decision.

When Ted and Barney jeopardize Robin's new relationship by professing their love for her, Robin realizes that she is finally over them. Meanwhile, after spending a weekend sleeping in twin beds, Marshall and Lily decide to get twin beds at home.

When Ted, Marshall, Lily and Barney crash a highfalutin party at a swanky New York apartment, Ted gets the chance to mingle with the snooty guests and show off his intellectual side.

When Ted takes a date to see a new hit movie, "The Wedding Bride," he is shocked to learn the story is loosely based on his life, and that it was written by Tony, the man Stella left him for at the altar.

Marshall and Lily make a secret pact to start trying to have a baby if they ever finally see Barney's doppelganger. Meanwhile, Robin finally gets an offer for her dream job.

When Ted and Barney argue about who has "dibs" on a hot girl, Ted realizes that she is there with Cindy, a girl he previously dated who is also the roommate of his future wife. Meanwhile, Robin is heartbroken over Don, and Marshall can't keep quiet about his desire to start a family.

When Barney convinces the gang to help his mom move out of her home, they quickly learn that she has been very protective of Barney and lied to him about events throughout his life. Meanwhile, Ted gets upset when Robin oversells him to a blind date.

Barney uses his best womanizing tactics to try to convince Ted to design the new GNB building; Robin drunk dials Don.

When the gang teases Robin about not being a real New Yorker, she sets out to prove them wrong by racing to catch a glimpse of Woody Allen.

Ted becomes conflicted after meeting an attractive woman who is passionate about saving the landmark building being torn down for his new project.

Marshall and Lily try to figure out how to conceive a baby with the gender of their choice; Robin's perky new co-anchor irritates her.

When Zoey enrolls in Ted's class, she manipulates his students into taking her side in the fight to save the building being torn down to make room for his project. Meanwhile, Marshall and Lily spot Robin marching in the Halloween parade of shame.

When the gang goes to a black tie event at the Natural History Museum, Ted gets introduced to Zoey's husband, The Captain.

Barney's discovery of a Canadian kids show called Space Teens, that Robin appeared on as Robin Sparkles, leads the gang to get her to reach out to her co-star, Jessica Glitter.

When Ted leaves the bar early to prepare a Thanksgiving feast for his friends, the gang winds up partying all night with The Blitz, an old friend from college who has bad luck. As a result Ted is forced to spend Thanksgiving with Zoey.

When Ted's new friendship with Zoey tests the theory that single men and married women can't be friends, he invites her husband, "The Captain," to hang out with them. Meanwhile, Marshall and Robin decide to spend alone time together, and Barney and Lily possibly have a fight.

Lily and Marshall receive shocking news that has a profound impact on the gang. Ted begins his duties as best man for an old friend's wedding.

Afraid they will never get pregnant, Lily and Marshall decide to see a specialist. Robin begins her new job.

While on a trip to Minnesota, Ted and Barney try anything to make Marshall laugh. Marshall runs into an old nemesis from high school.

Barney gets emotional when he opens up to Honey about his life. Ted admits to having feelings for Zoey to the group.

Barney declares February 13th a holiday for desperate women. Marshall receives a Valentine's Day surprise from Lily. Zoey and Ted work on figuring out their relationship.

Marshall becomes obsessed with saving the environment after seeing a documentary on garbage. Ted runs into The Captain. Barney admits he has feelings for a woman.

When Barney starts to have real feelings for Nora, he worries that something is wrong with his heart. Meanwhile, Robin starts dating a guy who acts a lot like a dog.

Barney meets his father and is shocked by the differences in their lives. The rest of the gang learn their "gaps"; knowledge they should have by now, but don't.

Lily and Barney react badly when Marshall finally quits his job at Goliath National Bank to take a volunteer position at an environmental organization. Meanwhile, Ted and Zoey's opposing positions on the future of the Arcadia come between them.

When Barney tries to bond with his father, he asks the gang to help make his life seem more exciting by lying about their own lives. Meanwhile, Robin runs into a guy she has a crush on.

When Marshall and Barney argue over the destruction of the Arcadian Hotel, Robin and Lily try to mix the right combination of cocktails that will force them to make up. Meanwhile, Ted plans a romantic weekend away with Zoey.

When Ted is faced with an important decision that might affect his future with Zoey, the gang expresses their true feelings about her.

Robin and Barney bond when they intervene in Ted's relationship, and Marshall and Lily watch a ticking clock as he fears that he soon will be the victim of food poisoning.