HOW I MET YOUR MOTHER returns for a hilarious fourth season! It all started when Ted's best friend, Marshall, dropped the bombshell that he was going to propose to his long-time girlfriend, and now wife, Lily, a kindergarten teacher. At that moment, Ted realized that he had better get a move on if he too hopes to find true love. Helping him in his quest is Barney, a friend with endless, sometimes outrageous opinions, a penchant for suits and a foolproof way to meet women. When Ted met Robin, it was love at first sight, but when things didn't work out, Ted realized destiny must have something else in store. The series is narrated through flashbacks from the future.
After Stella accepts Ted's proposal, Ted realizes he knows shockingly little about his bride-to-be. The two spend time getting to know each other better, and Ted tests their true compatibility by having Stella watch his favorite movie, Star Wars, which she has never seen before. Meanwhile, Lily learns Barney has feelings for Robin that he has been keeping bottled up all summer. Thrilled with the new, warmer Barney, she sets out to help him express them.
When Marshall reminisces about finding the best burger his first night in New York but not being able to find the restaurant since then, the gang sets out on a mission to find the legendary burger. But as the search grows futile, Marshall becomes overly fixated in finding the burger, making the gang question if this has more to do with him not being able to find a job and the toll it’s taking on him.
Tired of spending most of his time on the train commuting to Stella’s in New Jersey, Ted convinces the group to hang out at her place one night, even though they hate New Jersey. While at Stella’s, Ted tries to sell the gang on how great it is but when he learns Stella expects him to move to New Jersey after they’re married, Ted has a change of heart about the Garden State. Also, Robin gets a job at a CNN-style news station and quits her old job. However, after quitting she finds out she didn’t actually get the job, only an audition. In the end, Barney and Lily help Robin regain her confidence and she winds up with a big career opportunity to be a foreign correspondent in Japan.
In packing up the apartment to move out for good, the gang starts to get cold feet. While sorting through old stuff, Ted discovers that at one point Marshall and Lily were going to stage an intervention to tell him not to marry Stella. After admitting they thought Ted and Stella were moving too quickly but now realize they were wrong, Ted then starts to question if maybe his relationship is moving too fast. His hesitation towards change then makes Marshall and Lily question whether they should move into their apartment, and Robin becomes uncertain about taking the job in Japan.
When Stella’s sister’s rustic wedding falls apart, Ted and Stella step in to get married with only a few days’ notice. Despite the short notice, Robin catches a flight back from Tokyo. But when Stella finds out Ted invited Robin, the divisive issue of whether an ex should even attend a wedding threatens to overshadow everything. In an effort to make Stella okay with Robin attending, Ted winds up inviting Stella’s ex, Tony, and in the end learns the hard way why it’s not a good idea to invite an ex to your wedding.
After being left at the alter, Ted tries to pretend it didn’t happen despite his friends' concerns that he hasn’t dealt with his emotions. They take steps to try to get him to open up. But only a chance crossing of paths with Stella herself finally allows Ted to see that he has major unresolved issues and he sets out to confront her about everything that happened.
Marshall and Lily consider whether or not they’re ready to have a baby. After deciding they’re ready, Lily panics and turns to Ted and Robin for advice since they have very different points of view on the subject. And, after finding out he’s not going to be a father, Barney creates "Not A Father's Day," a new holiday that celebrates single guys everywhere.
When the company Barney works for needs an architect to design its new headquarters, Barney gets Ted a shot to throw his hat in the ring and pitch his ideas. But when Barney prefers a flashy Swedish design over Ted’s, Barney has to decide whether friendship or business is more important. Meanwhile, Robin rediscovers the “Woo Girls”, the single party girls, and Lily feels left out as a friend.
When Ted walks in to find Robin’s date sitting on the couch naked, he stumbles onto a phenomenon that revolutionizes the gang’s concepts on the art of seduction. For Ted has discovered “The Naked Man”: a move on a first date that involves waiting until the woman leaves the room and then stripping nude in hopes that when she returns, she’ll be charmed by the man’s bravado and decide to sleep with him.
When the bartender at MacLaren’s gets into a fight with some patrons sitting in the gang’s favorite booth, Ted and Barney decide to back the bartender up and get into their first fight. Ted wants to prove he’s not the pathetic guy who got left at the alter and Barney wants to impress Robin, who thinks fighting is sexy. But when they step outside and find the bartender, Doug, has knocked the guys out in a flurry and thinks Ted and Barney helped him do it, Ted and Barney decide to go along with the legendary story. The story of the fight makes them heroes at the bar until the guys who got beat up decide to press charges, and Ted and Barney have to decide whether or not to come clean.
When Ted’s younger sister, Heather, comes to visit and decides she wants to move there, Ted worries that she’s not mature or responsible enough to survive in NYC. Being the overprotective older brother, Ted tries to keep her out of trouble, and in particular keep her away from Barney. But when Ted becomes too overbearing, Heather teaches him a lesson that gives him new respect for her. And after northern natives Marshall and Robin bond during the first frost of the year, Marshall helps Robin get through her worst bout of homesickness by introducing her to his favorite Minnesota themed bar.
Robin and Ted navigate being exes who are now roommates and discover they get along better when they’re sleeping together as “friends with benefits”. Barney is trouble by the news and has a hard time dealing with his emotions. In an effort to reduce Ted and Robin’s roommate conflicts and stop them from sleeping together, Barney helps out around the apartment, leading Ted to suspect something is up and confront Barney about his feelings towards Robin. Also, the bathroom situation at Marshall’s work is super-stressful, and as a result he has trouble doing certain business there.
When a snowstorm hits the city before Lily returns from a teacher’s conference in Seattle, Marshall and Lily agree to forego they’re longstanding airport reunion ritual. But when they each start to worry that letting another ritual retire means that their relationship is losing its magic, Marshall enlists Robin’s help to get to the airport in time while Lily tries to pick-up a Seattle souvenir for Marshall, all in the middle of a blizzard. Meanwhile, Ted and Barney are meeting two women at MacLaren’s, so when Carl threatens to close up because of the storm, they offer to watch over the bar until the women show up. After having fun tending the bar, things get out of control when the girls arrive with their thirsty band-mates.
Robin discovers that she only has four days to find work as a television reporter or she will be deported back to Canada. Willing to try anything to avoid deportation, she agrees to let Barney produce a new reel and video resume for her, but pulls the plug on the project when Barney’s directions become too ridiculous. However, Barney comes through for Robin in the end, after putting together a video resume from footage they filmed before Robin walked out. Meanwhile, Ted, Lily and Marshall update their own resumes to more accurately depict their credentials.
After noticing some bizarre and elusive behavior from Barney, the gang starts to suspects that he may have found a girlfriend. When he mysteriously leaves MacLaren’s during drinks they decide to follow him, and they discover that he’s actually been secretly visiting his mother. However, they also discover that Barney has convinced his mother that he’s married and has a son, and that he’d hired actors to portray them. After barging in on Barney with his “family,” the gang has no option but to play along, until Ted gets caught cheating with Barney’s “wife.” Meanwhile, Lily admits to Marshall that she hates his mother, while Robin commiserates with the old soul portraying Barney’s “son.”
When Lily and Marshall hear that Ted’s college girlfriend, Karen, has moved to New York City, it immediately becomes clear that they can’t stand her. They tell the gang about how pompous Karen was and how she cheated on Ted. They insist that Ted stay away from her, but soon find out that Ted has not only already called her, but that they have gotten back together. Meanwhile, Marshall tells a story about forgetting to bring dress pants to work which Barney finds hilarious.
When Ted’s girlfriend Karen finds one of Robin’s earrings in his bed, she accuses him of cheating on her and breaks up with him. Ted soon learns that Lily, who couldn’t stand Karen, planted the earring in his bed in order to break up the relationship. Ted goes on to discover that Lily had actually broken up several of his relationships, and had even been behind his break up with Robin. Meanwhile, the gang all gathers at Lily and Marshall’s to watch Robin’s new early morning news show, and Barney discovers how comfortable sleeping in a nightshirt can be.
Marshall and Barney lie to keep Ted from finding out the headquarters he'd been hired to design for GNB has been cancelled.
When Barney is banned from Laser Tag, he plans to get revenge by TPing the Laser Tag center and asks Ted to help.
After losing his job, Ted forms his own architecture firm which he sets up in the apartment he shares with Robin.
Ted meets a new girl, Holly, and the gang insists that he wait three days before calling to ask her out. Ted reluctantly agrees, but decides that texting her before then is fine, and he strikes up a text conversation with Holly that lasts several days. However, he soon discovers that he is actually texting with Marshall and Barney, who had swapped Holly's number in Ted's phone for Barney's to keep him from calling her before the three days was up. Furious after discovering the truth, Ted goes ahead and calls Holly to ask her out, and discovers that the three day rule is more apt then he once suspected.
Ted explains to his future children that being in the right place at the right time can have a massive impact on a person’s future, and that the universe tends to have a way of pushing a person toward their destiny. He presents an example where seemingly unimportant and unrelated occurrences in Robin, Marshall and Barney’s lives lead him to an unexpected encounter with Stella, which sets him on the path to meeting his children’s mother. Meanwhile, Robin suffers through a bout of food poisoning, Marshall deals with an addiction to graphs and charts and Barney celebrates his 200th female conquest.
After Ted bumps in to Tony and Stella on the street, Tony shows up at Ted's apartment and insists on taking responsibility for his part in Ted being left at the altar. He explains to Ted that his family is very wealthy and can help him with his career, but Ted tells him he has no obligation to help and that the past is behind them. However, Tony won’t give up trying to help and finally Ted goes off on him, insisting that he is happy to have Stella out of his life because she is such a terrible person. Tony reflects on this and ends up breaking things off with Stella himself. Stella then asks Ted to talk to Tony for her, to convince him to take her back. Meanwhile, after finding out that Marshall and Robin have successfully gotten themselves out of speeding tickets, Barney gets intentionally pulled over several times to prove that he can as well.
In a last ditch attempt to bring business to his fledgling architecture firm, Ted stays up 24 hours straight working on an pitch. With Ted refusing to leave his work, Marshall tries to lure Ted to the roof for a surprise 31st birthday party. However, before he makes it up to the roof, he is attacked by the goat Lily had rescued and left in the bathroom. After ending up in the hospital, the entire ordeal helps Ted realize that he needs to explore other career options, and he decides to take a job as a professor. Meanwhile, Barney finally decides to admit to Robin that he has feelings for her however, he is thrown when she beats him to the punch and says she is in love with him. Also, Marshall contemplates finally taking the leap from their building to a neighbor’s roof.