To calm an anxious Robin on her wedding day to Barney, Ted recounts the story of how he persuaded Victoria to write a left-at-the-altar note to her ex-fiance Klaus explaining why she ran out on their wedding. Meanwhile, Barney attempts to hide the fact that he and Robin used to date from Quinn, but Quinn learns the truth when sleep-deprived Marshall and Lily accidentally blurt it out.
Barney prepares a comprehensive pre-nup, causing the other guys to think about relationship amendments for their significant others. Tension sparks among the couples when Quinn sets up her own pre-nup proposal.
Lily and Marshall have trouble finding a nanny when Barney comes up with an elaborate scheme to meet girls. Meanwhile, Robin and Ted fight over whose relationship is more serious.
When Lily and Marshall can't decide on whom to appoint as godparents for baby Marvin, they put the gang to the test to see who would be the best choice.
As the season of break-ups continues, Ted and Victoria must choose the next step in their long and complicated relationship. Meanwhile, Robin worries about Barney when he chooses a dog to be his wingman.
Barney helps Robin break up with Nick, when she is hesitant to do so herself. Meanwhile, Lily and Marshall desperately look for some time alone.
Marshall recommends his old law-school classmate Brad (Joe Manganiello) for a job at his firm, but the interview goes awry, and Marshall must do damage control with his boss. Meanwhile, Robin helps negotiate Barney's return to the strip club circuit.
Marshall competes against his old friend/new nemesis Brad in the most important court case of his career. Meanwhile, the rest of the gang reminisces about their run-ins with the law as teenagers; which leads to a debate over who was the biggest delinquent.
A determined Robin goes to great lengths to get back together with Barney. Meanwhile, Ted substitutes as Marvin's nanny, leading Marshall and Lily to realize that Ted is using baby Marvin as a replacement for his other baby, the GNB building.
Robin becomes suspicious of Barney's motives for dating Patrice. Meanwhile, Marshall and Lily are disturbed by the fact that his widowed mother begins dating her father.
Robin takes steps to have Patrice fired from WWN, while Marshall puts a jinx on Barney. Later, Ted invites his architecture professor to the dedication of the GNB building, and Marshall and Lily bump into an oddball acquaintance from college.
Christmas approaches and Ted wrestles with whether to tell Robin about Barney's intentions involving Patrice, while Marshall and Lily get an early Yule gift, a night away from Marvin, but a case of separation anxiety strikes and threatens to ruin the evening.
Robin wants Barney to ask her father for permission to marry her. Lily and Ted feud about planning the wedding, which gets Ted to admit his regrets about letting go of Robin and Lily to confess her regrets about motherhood and her career. Baby Marvin's bout of constipation stresses Lily and Marshall.
Even though Ted and his new girlfriend share none of the same interests, Barney urges Ted to sleep with her, until they find out she is Barney's half-sister. Meanwhile, Robin is adapting to her new status as an engaged woman.
While trying to find out the identity of the person with whom Robin was once obsessed, Barney uncovers the 'Robin Sparkles' episode of the music-documentary series Underneath the Tunes. Marshall and Lily are concerned that Ted's latest girlfriend might be stalking him.
Ted is reluctant to break up with his girlfriend Jeanette despite her unstable behavior, and Lily offers him advice. Meanwhile, after an adventurous experience babysitting, Robin finally overcomes her fear of holding baby Marvin and becomes emotionally attached to him. Guest starring Mike Tyson.
Zoey's ex-husband, The Captain, unexpectedly calls Ted, and the gang reminisces about what happened when they last saw him a year and a half earlier. Lily gets a surprising new career opportunity when The Captain offers her a job as his art consultant.
After Ted and Jeanette part ways, Barney steps in as matchmaker using the supposedly-destroyed Playbook. Meanwhile, Marshall has some embarrassing moments at an art gallery opening where Lily is battling to make a good impression.
Barney reluctantly attempts to sell his apartment by holding an open house, during which Ted and Marshall get mistaken for a couple. Tension arises between Lily and Marshall when her new job causes her to spend less time at home.
Ted and Barney's future versions attempt to persuade present day Ted to go see Robots Versus Wrestlers. Marshall challenges Robin to a dance-off after she is given credit at MacLaren's for a cocktail he invented.
The Captain asks Lily to relocate to Rome for a year to work as his art consultant, but she is afraid Marshall will resent her if she agrees. Ted and Barney notice a beautiful woman wearing a puffy coat and become obsessed with finding out what she's hiding.
The gang brainstorms to plan the ultimate bachelor party for Barney.
Robin desperately tries to locate the antique locket that she buried in Central Park (when she visited at 14 years old) to wear as her "Something Old" for the wedding. Meanwhile, Marshall and Lily ask Ted to help them pack for Italy and Barney invites Robin's father to play Laser Tag in order to bond with him.
As the gang prepares to go to Robin and Barney's wedding, Ted invites Lily to see the final renovations he made on his house in Westchester. Meanwhile, Robin and Barney's night of relaxation is ruined by an obnoxious couple and Marshall takes baby Marvin on a last-minute trip to visit his family in Minnesota. The episode concludes with The Mother onscreen for the first time.