The sixth season of the American television comedy series How I Met Your Mother premiered on September 20, 2010, to conclude on May 16, 2011 on CBS.
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.
Barney convinces the gang to come to his childhood home to help his mother Loretta move out.
Barney re-offers Ted the job of designing the new GNB Tower, a project which had previously been put on hold. Ted declines his offer and says he is content with his life as a Professor now and could not face the disappointment of the project falling through again. Barney proceeds to try and “get the yes” from Ted by using all of his best womanizing tactics, including using Marshall as his wingman. After finally confronting Barney about his attempt to “seduce” him into the job, Ted realizes that designing the building is his dream and accepts the job. Meanwhile, Robin is still not completely over her relationship with Don and drunk dials him. Lily attempts to convince her to delete Don from her phone and they realize how hard it is to completely close the book on some things from your past.
Using all different modes of transportation in Manhattan, the gang races to see who can get to a restaurant downtown fastest to see Woody Allen, each facing obstacles along the way, each one needing to win for their own very significant reasons.
Ted is torn after meeting activist Zoey (guest starring Jennifer Morrison) whose passion is saving a landmark building that is to be torn down, and be replaced by the new GNB building, that Ted is, unbeknownst to her, designing.
Lily and Marshall visit their friends Claudia and Stuart who have just had a baby only to discover the couple has not yet named the baby because they can’t agree on a name.
Marshall, already ambivalent about working for GNB, a corporate shark that fires people with no regard, refuses to fire his assistant Randy even though Randy is terrible at his job.
The gang is attending a black tie event at the Natural History Museum, thanks to GNB. Much to Ted’s surprise he runs into Zoey, his nemesis; she is the wife of a huge GNB client, boat enthusiast, self nick-named, the "Captain." Ted is shocked to find out Zoey is the rich trophy wife of this older man.
Barney discovers a copy of Robin's failed Canadian children's series that she starred in as Robin Sparkles called "Space Teens" about two teenage girls who solve crimes (with the help of Alan Thicke) in space using math.
It is the night before Thanksgiving and the gang is at McClaren's hanging out. Ted decides he is going to call it a night as he is preparing Thanksgiving dinner for everyone the next day and is going to make his "Turturkeykey" which is a turkey stuffed inside another turkey.
Ted befriends Zoey's husband, "The Captain," when he begins to question his own relationship with Zoey.
Upon hearing the news that Marshall and Lily test positive from a home pregnancy test, the gang assesses the meaning of their lives. Lily and Marshall freak out about the news and start to panic about becoming parents and question if they are ready to have kids. They soon discover they are not really pregnant, and are surprisingly happy about it which sends everyone into a tailspin. Robin debates whether she should take a job as the "coin toss" girl on a TV game show hosted by Alex Trebek or accept the offer to be a researcher position for the World Wide News, which has always been her dream. Barney debates how he should spend his hefty bonus- on frivolous gifts ala Oprah, with "Barney's Favorite things," and a diamond suit or whether he should donate it to the church organization that helps outfit the less fortunate for job interviews. Meanwhile, Ted has been trying to help his friend Punchy plan his wedding since he is best man and Punchy panics that he may not be ready to get married. However, as the gang waivers about these decisions, Ted loses it and encourages everyone to embrace the Christmas spirit and sets everyone straight, encouraging them all to make the right decisions- Robin accepts the news job, Marshall and Lily embrace having kids, Punchy gets over his cold feet and Barney donates all his suits to charity.
Marshall and Lily still not pregnant, go to see a fertility doctor, Dr. Stangel, who turns out to be Barney's doppelganger. After accepting that Dr. Stangel sis actually not Barney in disguise, he is able to examine Lily and finds she is very fertile, and that Marshall may be the problem. After failing to produce a sample at the doctor's office, Marshall races home for some privacy only to discover his parents are there having shown up unexpectedly for a visit. Unable to focus on his task with his parents there, he and Lily finally tell his parents the truth about what is going on. It turns out Marshall's sperm is fine and he celebrates his virility with the gang at the bar. Knowing his parents are awaiting his results Marshall goes outside to call his dad with the good news, but there is no answer. Meanwhile, Robin has started her job at World Wide News as a researcher and discovers that her old co-anchor Sandy Rivers is hosting one of their shows, "Hardfire". Sandy shows the staff a slew of embarrassing clips from Robin's past including "Robin Sparkles" In the end, Robin is able to embrace the teasing and deflates the power Sandy had from picking on her.
The gang is in Minnesota for the funeral of Marshall's father Marvin Sr., each trying to find the appropriate role to help Marshall. Robin is the "vice girl" armed with a purse filled with everything from booze to cigarettes to pills. Lily's job is to allow Marshall's mother to pick on her so that she can take care of her, allowing Judy who has been going non-stop, to finally relax. Ted and Barney try to cheer up Marshall with videos of men being hit in their privates. Making matters even worse for Marshall is that his childhood nemesis Trey, who is as annoying as ever, is conducting the sermon, the theme being "last words". Marshall is frustrated as he recollects different moments to determine what his father's actual last words to him were. His last conversation with his father was petty and somewhat insignificant compared to those of his other family members. However, Marshall eventually realizes he has a voicemail from his father that he had not listened to because his phone had been dead. When he finally gets the courage to listen, he realizes his father's final words to him were "I love you." This experience leads each of the gang to call their father that night after the funeral and Barney calls his Mom and tells her he is ready finally to meet his father.
Zoey offers to set up Ted up with her cousin, a naive girl who the gang starts to refer to as Honey because her gullible nature makes you want to say "Oh, Honey." However, Ted does not go home with Honey but instead lets Barney make his move. Zoey is thrilled upon hearing the news that Ted did not hook up with Honey. Now realizing he has feelings for Zoey, Ted tries to end their friendship, not wanting to complicate things because she is a married woman. When Zoey demands to know the reason, he ends up accusing Lily of hating her. After confronting Lily, who then blames Robin, who then blames Marshall- Zoey realizes it is Ted who is pushing her away and he refuses to tell her why. Meanwhile, Marshall is still in Minnesota and has been told all versions of the story, including a surprise call from Honey who confides in him that Zoey is getting divorced, and he pieces all the information together to discover Ted and Zoey are in love with one another.
Barney declares February 13th as a new holiday "Desperation Day" in which single women throw themselves at men in fear of being alone on Valentine's Day. Robin and her single friends from work are at the bar that night in an effort to prove they don't care about the upcoming holiday. Barney finds himself quite taken with Robin's friend Nora. Thanks to Robin, she forfeits her role in his laser tag tournament the next day, and sends Nora to join him which results in Barney having a date on Valentine's Day after all. Meanwhile, Marshall is still in Minnesota consoling his mom. Lily misses him and decides to go to Minnesota to surprise him for Valentine's Day, which they have not spent apart since they met. Lily is surprised to find Marshall has reverted to childlike behavior having his Mom wait on him hand and foot. He refuses to leave with Lily and is driving his mother crazy. Meanwhile, Ted and Zoey's relationship starts to get more serious and an overwhelmed Ted shows up in Minnesota. He and Marshall realize they are both running away, too scared to face reality. With all flights cancelled, they drive back to NY together just in time for Valentine's Day.
Marshall is back at work after his father’s death feeling apathetic about working at GNB and completely disinterested in having sex with Lily. However, after watching a documentary about “Garbage Island” an island in the Pacific half the size of Texas that is used as a landfill, he becomes obsessed with saving the environment. Marshall forces his new views on McLarens who begin recycling much to the dismay of Wendy the waitress who must now carry the bottles to the recycling facility after work every night. He also makes a presentation to GNB which will cost the company millions of dollars and results in one of his colleagues getting fired for supporting it. Eventually Marshall realizes he is using this cause to find meaning in his life and Lily gives Marshall her blessing to quit his job at GNB to pursue his dream of practicing environmental law. Meanwhile, Barney is offended that after his laser tag date with Nora she did not go home with him and tells Robin that he refuses to pursue her. However, when Robin leads him to believe that Nora has met someone else, Barney admits he really likes her and gets her number to call for a second date. Ted volunteers to go pick up a box of Zoey’s things from her old apartment as she fears running into her ex-husband, The Captain. Ted runs into him in the lobby of the building and is invited up to his study where The Captain confides in Ted about the end of his marriage, and that he knows Zoey left him for someone else. After convincing The Captain it was not another man who is to blame for his marriage ending he admits that he is the one now dating Zoey.
After the death of Marshall's father, the gang decides to all get their hearts checked out by a doctor. Barney has a slight irregularity and must wear a heart monitor on his date with Nora. Through the doctor's analysis of his EKG, we learn that Barney has true feelings for this girl but is too afraid of a serious relationship. Meanwhile, Robin starts dating a guy "Scooby" who ironically acts just like a dog.
Barney’s father Jerome finally responds to Barney’s letter and shows up at his front door. After learning his father is nothing more than a suburban driving instructor, Barney decides he wants nothing to do with him. However, the he gang convinces Barney to give him another chance, he agrees to go to Jerome’s house for dinner with his wife and son. Ultimately, Barney reveals he is not upset that his Dad is not the cool guy he had hoped but actually is hurt that Jerome now has the traditional family he always wanted.
Marshall finally quits his job at GNB and takes a volunteer position at an environmental organization. Lily tries to support this decision but eventually snaps, contemplating a whirlwind trip to Spain. After Zoey is able to get enough signatures for her petition to stop the building of the new GNB headquarters which would destroy an historical landmark, Ted realizes how difficult it is to be with a non-supportive partner. Meanwhile, Barney is distraught over Marshall's leaving GNB but while Robin is convinced it is an emotional response to abandonment issues, it turns out he is just angry he can not play a practical joke on him that he had been planning for months.
When Barney's father Jerry reaches out to spend time with him, Barney plans a wild night in the city in hopes of finding some connection to his very boring suburban-driving instructor Dad. Barney invites the gang, asking them all to play more exciting versions of themselves in an attempt to impress Jerry. However, after their crazy night of partying ends up with Barney and Jerry being arrested, Jerry admits that he faked being drunk in an attempt to bond with Barney and Barney realizes he may be getting closer with his father after all. Meanwhile, Robin runs into her “crush” whom she met in a department store years ago only to have the moment ruined by Ted who, per Barney's instructions, is pretending to be Robin's boyfriend.
After leaving his job, Marshall is given a horrific referral from GNB to an environmental law firm and decides to get even by representing Zoey in her efforts to save the Arcadian hotel. Barney feels betrayed by Marshall and the two get in a huge fight which results in their getting the entire gang banned from the bar. The girls decide the best way to get them to make up is to get them drunk; paying close attention to the effects different alcohol will have. In the end, after many rounds of different drinks Barney and Marshall make up, however the next morning they wake up not remembering any of it, and remain at odds. Meanwhile, instead of the romantic getaway they had planned, Ted takes Zoey to stay at the Arcadian for the night to prove that this run down rodent infested building is not worth saving. Zoey tries her best to endure it, but ultimately admits to Ted that she grew up at the Arcadian and it is a part of who she is. All making sense to him now, Ted decides to support her in saving the Arcadian.
Ted must decide to testify whether or not the Arcadian is a landmark in front of the Historical Preservation committee. While professionally he believes it is an eyesore, his personal conflict is between siding with his girlfriend Zoey or his best friend Barney. Ultimately, he realizes he must do the right thing and advocates the building's destruction but is blindsided when Zoey produces an audio recording of Ted saying just the opposite. Ultimately, when "vandals" remove iconic stonework from the building the committee decides it is no longer worth preserving. Ted also realizes after her betrayal that Zoey is not the woman he will spend the rest of his life and breaks up with her confirming she is not the "Mother" in this story.
Ted starts to feel pressure and insecurity as plans for the Arcadian get underway and Barney and Robin are fearful that this will drive him to get back together with Zoey. When Ted is nowhere to be found, Barney and Robin follow a trail of clues to Brooklyn so they can stop him from making a big mistake and are able to catch him in the nick of time. Meanwhile Lily gets horrible food poisoning from a grungy deli she and Marshall like and Marshall, who ate the same thing a few hours later, becomes concerned that the same fate is upon him. Things get worse when Marshall gets a call to come in that day for his dream job interview at an environmental law firm and must figure out how to make it through the interview without getting sick.