Trama

Maggie a girl next door Ted has wanted to date for years has suddenly broken up with her latest boyfriend, giving him and many other guys a chance to score with her.

Ted has always thought that Maggie Wilks, a woman he and Marshall and Lily knew in college, is the perfect woman. He's wanted to date her ever since she moved to New York, but she's always been in a relationship. Even between relationships, it's been a matter of hours before she was with another man in a long term relationship. So when Ted finds out, with the help of Maggie's cooperative neighbor, that Maggie is once again single, Ted rushes over to her apartment before another man swoops in. He gets there in time. As Ted forgot that he has a class to teach for the time that he and Maggie are supposed to go on their first date, he asks Marshall and Lily to keep her away from any men until he returns. That plan goes slightly awry when Marshall, reading through an old letter he found that he wrote to his 30 year old self when he was 15, hits a sudden and early mid-life crisis, to which he and by association Lily have to attend. They leave Maggie in Robin's care. When Robin has to attend to another crisis in helping Ted, she leaves Maggie with Ted's worst nightmare: Barney. Will Barney respect Ted more than Maggie's babiliciousness? Meanwhile, the discussion in Ted's class that evening is a little different than in a standard architecture class.—Huggo

The gang tries to help Ted when the perfect girl is finally available, and Marshall takes action when he finds a letter written by his younger self.—CBS Publicity

Marshall stops by Ted's apartment with a box of childhood memorabilia from his mother (Old book of Mad Libs). Ted receives a call from an old woman telling him "the window is open", and races over to a woman's apartment a few blocks away. Later at MacLaren's, Ted explains that "the window" was the window of opportunity to date a woman named Maggie (Joanna García) (who Ted remembers as the perfect girl for him.. They went to college together and she was the ultimate girl next door), who followed up every long-term relationship with a very short break, and then an even-longer relationship.

Ted had known Maggie, the "ultimate girl next door", since college, but she has always quickly found a new boyfriend after being single. Every guy who dates her, falls madly in love with her. Since Ted met her she has only been single for 3 brief windows of opportunity.

After several failed attempts (first guy Maggie dated for a month, the next guy for 2 yrs and the one after that for 3 yrs. This time Ted was at her door 1 hr after her breakup. All she did was check her mail and fell in love with the mailman. She dated that guy for 4 yrs) Ted begged Maggie's neighbor, Mrs. Douglas (Barbara Perry), to tell him the moment she was single again. Ted arranges to meet her at the bar, and is determined not to screw up this time to make sure she comes in contact with as few other men as possible, even ordering her a taxi with a female driver. Robin reminds Ted he still has to teach his evening class, and he is forced to leave Maggie with Marshall and Lily. Clear instructions are given to them: no waiter takes her order, no busboy clears her table, if she bursts into flames a female firefighter puts her out.

While his class counsel's Ted on finding love, Marshall rifles through his childhood belongings at the bar. He finds a letter to himself from 1993. The rat-tailed, overalls-wearing 15-year-old insists that Future Marshall get an expensive vehicle, a hot wife (blonde, 6 feet tall with an awesome rack), has a rat tail, can slam dunk and that he never "sell out". Marshall mournfully reflects that his job at Goliath National Bank is the ultimate sell-out. Meanwhile Barney has taken the challenge to sleep with a girl while having Marshall's overalls on. Robin keeps cock-blocking him by making him look like a farmer jokes all night.

Marshall leaves MacLaren's, and Lily chases after him, leaving Maggie with Robin. Under Robin's watch, a coworker of Maggie's, named Jim (Jamie Kaler), slips into the booth. Robin shamelessly flirts with Jim (laughs at his jokes, spills wine all over her top and her boobs) and butts in on his invitation to take Maggie to an art show, trying to keep him distracted. Robin passes Maggie off to Barney, who has dared himself to get laid wearing Marshall's old overalls. Ted races back to the bar, only to face Jim and Barney, who both want Maggie.

Lily heads to GNB, thinking Marshall is about to quit his job, but upon further inspection of the letter, she finds another thing that young Marshall was proud of: his ability to dunk a basketball. On the GNB basketball court, Marshall explains how sad he is to have never reached his dreams, but Lily insists that he has led a wonderful life. He attempts to dunk and injures himself. Lily offers to make it up to him and have sex in his office, unable to move, he suggests instead they have sex right there on the court.

Robin covertly sends Maggie back to her apartment while the three men bicker over who should get first crack at Maggie. They race to her apartment door, and they find she has reunited with her childhood neighbor, "the guy next door." Future Ted briefly retells their long-standing romance, the second-greatest love story he's ever heard (Maggie & David had grown up together and were separated when David's family moved away. David came to NYC and the first thing he did was to look Maggie up), and flashes forward to their married bliss. Maggie's window never opened again. When Ted exits the apartment building, he tells Barney he's ready to find true love again. Barney then sleeps with the old woman in Maggie's building to complete his overalls challenge.

Marshall returns to the bar to write a letter to himself 29 years further in the future. In the letter, he makes a small request for his future self to let him know if time travel exists. Lily returns to the booth with a free plate of hot wings, which she says someone "sent back" because they were too hot. Marshall finishes the letter, telling Future Marshall that so long as he is still with Lily he will be doing all right. As it turns out, an older version of Marshall is on the other side of the bar, who apologizes to Wendy the Waitress for sending the wings back, saying he "already had some wings earlier... much earlier".