In season 2 Ted was at the top of his game, working as a successful architect and deeply in love with his girlfriend Robin. In the season finale, while Ted's roommates - best friend Marshall, and Lily, his new wife, head off to their honeymoon, Ted and Robin reveal the sad news of their break-up to Barney, their friend with endless, sometimes outrageous opinions, a penchant for suits and a foolproof way to meet women. At first Barney is shocked and saddened by their revelation, but he doesn't waste any time and starts planning Ted's return to single life... which Barney insists will be "legendary!" So as season three begins Ted's search continues to find true love...
To Barney's dismay, Ted wants to take a few weeks after his breakup with Robin before getting back out on the dating scene. But when Robin returns from her vacation with Gael, an incredibly hot Argentine surfer-massage therapist, Ted overcompensates with a night on the town that's a little too legendary even for Barney's taste, leading him into the arms of Amy, a somewhat unhinged punk rock girl with a taste for tattoos. Meanwhile, on a double-date with Robin and Gael, Marshall and Lily are determined to hate Gael, but his charms prove difficult to resist.
Now that she has spent some time at home with Gael, the hunky Argentinean guy she met while on vacation, Robin begins to realize that he may not be such a perfect fit in her real life. Ted and Barney, however, see Gael as a chick magnet and pose as foreigners so that they can meet more women. Unfortunately, their plan backfires when they realize that the women they attract when pretending to be tourists aren't actually from New York themselves. Meanwhile, Marshall and Lily have their first fight as a married couple.
When Ted gets blown off by Barney and Marshall, he goes down to MacLaren's, where he meets a beautiful young woman who takes a shine to him. As luck would have it, her old college friend shows up unexpectedly and also shows interest in Ted. Unable to figure out who is the most interested, Ted calls Lily to help him figure it out, only to discover that both women are equally attracted to him. To complicate matters even further, both women want to take the party to Ted's place. Overwhelmed, Ted gets Marshall, Lily and Barney, all of whom are trapped in the apartment when Ted unexpectedly returns with his potential conquests, to band together and guide him toward his goal of "riding the tricycle." Meanwhile, Robin's fateful grooming decision to not shave her legs complicates her date with an awesome new guy.
Based on Lily's recommendation, Robin dates a single dad even though she is not particularly fond of kids. To her surprise, she bonds with the guy's 6-year-old son. However, as happens in many of her relationships, Robin soon decides that things are getting too serious and that she must find a way to break it off with the kid. Meanwhile, Ted and Barney go after the same girl to determine once and for all who has better game. Marshall tries to prove to the guys that even though he is married, he is still relevant and can prove helpful in their pursuit of female companionship.
Ted is dating a new woman, and he decides it's time to introduce her to the group. When she asks how they all met one another, the gang takes a trip down memory lane. But when Ted's new girl is jealous about not having a good "how we met" story with Ted, Ted reveals to her a huge secret from his past, one he's never told Marshall: how he and Lily really met. It turns out that Lily and Ted might have kissed, and it might not have been fate that brought Lily and Marshall together, which is what they've believed ever since they met.
Marshall has an interview at a notoriously evil corporate law firm and ends up being flattered, wined and dined and otherwise seduced into possibly accepting a lucrative job offer, thereby setting aside his dreams of working for the Natural Resources Defense Council. Lily tries to give Marshall guidance on his job selection, but what Marshall doesn't know is that Lily is a shopaholic and has major credit card debt, making her a less-than-impartial advisor. Meanwhile, after Barney discovers the existence of a porn star named "Ted Mosby," Ted and Barney head to the Adult Video Expo to find the impostor.
Marshall and Lily decide to buy an apartment and proceed to make every mistake in the book. While applying for a loan, Marshall discovers Lily's credit card debt, which leads to a huge fight that Ted is able to recreate, CSI-style, employing his deductive reasoning and clues around the apartment. Barney stumbles upon another use for an open house: it can be a great place to bring a hot, clingy chick you'd never bring to your real home.
Ted thinks he has found a great girl until the gang meets her and shatters his illusion of how wonderful she is by pointing out that she never stops talking. Once her flaw is revealed, that becomes all Ted can see in glaring clarity, which forces him to break up with her. Angered that Lily has shattered his illusion, Ted points out Lily's annoying flaw to Marshall, and in turn this leads to the rest of gang pointing out each other's flaws. Also, when Marshall loses his password to retrieve his bar exam results, Barney orchestrates an elaborate plan to "help" him recover it.
Over Thanksgiving, Robin and Ted experience a backslide that starts with a joke Ted makes about Robin's new, older guy, then leads to a fight, which leads to them sleeping together. The backslide forces them to question whether trying to remain friends after a breakup is too difficult. Meanwhile, Marshall has set the slap bet countdown clock to expire in the middle of Thanksgiving dinner, so throughout the day, he torments Barney about the slap that is inevitably coming.
The gang joins a gym, and there Barney runs into Rhonda, his mom's friend to whom he lost his virginity. He learns that the night in question was built on a lie: she only slept with him because his brother bribed her. His confidence destroyed, Barney tries to bounce back with a trip to the Victoria's Secret Fashion Show after-party, but gets "the yips," losing his ability to pick up on women. Realizing he has to make it with Rhonda for real so that he can return to his former self, Barney sets out on a mission. Meanwhile, Lily and Marshall struggle to deal with Marshall's overzealous trainer, and the gang discovers Ted's workout regimen isn't exactly as strenuous as their regimen.
As Ted prepares for a date with the doctor who's going to remove his tattoo, Barney and the gang try to warn him that he may be breaking a cardinal rule of dating, "The Platinum Rule": don't poop where you eat. Whether it's your apartment building, your workplace or the bar where you hang out, it's never a good idea to get into a relationship with someone you see on a regular basis. Barney uses stories of three such relationships that he, Robin and Marshall and Lily have each experienced to illustrate the nine steps that inevitably follow in any such relationship.
Ted goes out for a crazy St. Patrick's Day with Barney, and discovers how much he's changed. After Ted has what he considers the most legendary night, Marshall replays the messages Ted left on his voice mail when his cell phone accidentally pocket dialed, and after hearing snippets over the course of the night Ted ultimately realizes he was acting like a jerk and he doesn't want to be that guy. Also, Marshall, Lily and Robin spend the night in Marshall and Lily's new apartment, only to make their own shocking discovery that the apartment is crooked.
Ted has ten tattoo removal sessions to win over his dermatologist Stella and get her to agree to go on a date with him. After trying gambit after gambit to break through, including being extra nice to her receptionist (Britney Spears) only to have the receptionist misconstrue Ted's friendliness as attraction, Ted finally discovers why Stella has been hesitant to get involved. Ted must decide if he really is ready for a more adult relationship, and convince Stella of the same.
A Mysterious Woman is ruining Barney’s mojo by warning women to stay away from him. Only Lily has seen her, but before she’ll help him identify the woman, Lily forces Barney to go back and confront the girls who are most deserving of an apology. Using the NCAA tournament bracketology the gang takes the top sixty-four women Barney has been with and narrows the list down to The Final Four; the four women Barney must apologize to and face the repercussions.
When Marshall slips up at work and gets screamed at by his boss, he has a hard time facing the problem. The incident forces him (and the gang) to examine how to survive in a volatile workplace. Eventually, he must confront the real issue: Taking this job might have been a big mistake. And, Ted buys a new car to impress Stella but soon realizes how hard it is to keep clean with his friends around.
When an old flame from a Robin Sparkles love ballad video comes back into her life, Robin turns into the head over heels 16 year-old girl she was the first time around. While the gang tries to help Robin see what a loser the guy has become, Robin has a hard time letting go of her past crush. But when he breaks up with her again, it’s Barney who finally helps her to realize how awesome of a person she has become. And in a shocking moment between them, Barney and Robin sleep together.
As Ted prepares for his thirtieth birthday by getting rid of old stuff he’ll no longer need, Barney and Robin struggle with the ramifications of their night together and whether or not to tell Ted. Barney enlists Marshall’s legal expertise to find a loophole in “The Bro Code”, a list of do’s and don’ts for all bros, but ultimately decides he just needs to come clean. And in a surprise blow, Ted “breaks up” with Barney, realizing their lives are going in a different direction and he’s tired of the single life.
Ted is shocked to learn that Stella hasn’t been intimate with a man in over five years. With the help of the gang, Ted adjusts to the idea and prepares for a special night with Stella. However, Stella finds out that Ted shared her secret with his friends, which not only threatens their night together but their relationship as well. Ultimately they make up and Stella gives Ted something even more intimate than she was planning; she introduces him to her daughter, Lucy. Meanwhile, Barney struggles to adjust to life without Ted, adopting the socially inept Randy from his company’s mailroom as his new wingman.
As their expenses continue to mount, Marshall and Lily decide to sell some of their possessions online. In addition, Lily decides to also sell her artwork and potentially take another stab at her career as an artist. But when she can’t even sell her favorite painting, Lily begins to question whether it’s time to give up her dreams of being an artist. Also, Barney discovers Abby is the mystery girl who has been ruining his game with women. After reconnecting over how much they both hate Ted, Barney and Abby set out to show Ted how horrible he is in a relationship by doing lame couple-y things.
Ted has a brush with death which makes him reevaluate his relationship with Stella. Meanwhile, Marshall and Robin debate whether or not Ted's experience was a miracle. Robin doesn't believe in miracles but Marshall thinks they happen all the time and sites examples drawn from their lives to prove it. Ted and the gang are surprised when Barney doesn’t visit Ted in the hospital only to learn that Barney himself needs the biggest miracle of all.