Barney uncovers the lost episode of Robin’s “Underneath the Tunes” as Robin Sparkles. Meanwhile, Marshall and Lily are concerned that Ted’s new girlfriend is a stalker.
While riding the subway, Ted notices a woman reading the same book as he does (One Hundred Years of Solitude), however she leaves the train before he can even talk to her.
At the bar, Ted tells this to Marshall and Lily, then tells them that he listed a few details he remembered that would help him find her. They tell him that this is creepy and he should let that girl go. Ted tells them that this is destiny, but Marshall tells him that Lily and him meeting at Wesleyan was destiny, and what Jeanette did was crazy. He takes the pad (and the back-up pad) from him. However, the next day, he sees the girl outside the university where he teaches. He tells the gang that the girl's name is Jeanette. He tells them that she wanted to find him too, listing the things she remembered about him, which lead her to the university. However, she wasn't able to find his class and was going to give up when the fire alarm sent him out. Lily says that Jeanette is a stalker, but Ted tells her that there is a fine line between love and insanity, and explains a theory he came up with; The Dobler-Dahmer Theory. "If both people are into each other, then a big romantic gesture works: Dobler, but if one person isn't into the other, the same gesture comes off serial-killer crazy: Dahmer." He further elaborates by applying this theory on how Marshall asked Lily out by singing her a song he wrote. He further says that he was charmed by Jeanette finding him, thus she is a Dobler. Marshall and Barney tell him that they think that she was the one who pulled the fire alarm so she can meet him. However, Robin says that they shouldn't be so cavalier about the word "stalker". Barney thinks that she has a stalker and asks her about it. But Robin tells him that she was a stalker. Back in Canada, she liked a guy who wasn't interested in her and she got obsessed over him. She filled up her journals all about him and eventually got a restraining order put up against her. Barney says that she must have been a nut bag back then, but Robin says that she wasn't and agrees with Ted about there being a fine line and anyone can cross it and get obsessed. Barney asks her who the guy is. However, Robin tells him that she will only tell him about the guy if he admits that anyone can become obsessed.
Barney later breaks into Robin's apartment to read her old journals. He then flies to Canada to find the guy Robin was obsessed with. He then meets two of Robin's exes, neither of whom is the guy Robin was obsessed with. He then meets Simon. He tells Barney about a video documentary, "Robin Sparkles: Underneath the Tunes", which tells the whole story. Barney runs out of the restaurant to find the documentary. Barney then goes back to The Apartment and tells the others (minus Robin) that he found another Robin Sparkles related video. They watch the video, which tells the story of how Robin Sparkles changed, and includes talks with other Canadian celebrities about what happened at that time. The video explains that Robin cracked and wrote a grunge song P.S. I Love You as Robin Daggers, a darker alter ego. The song was so dark that Dominant Records refused to release it. The gang then see the video to the song and are shocked to see Robin's darker side. The video then shows Robin performance during the half time show of the 84th Grey Cup. Robin tells the spectators that Robin Sparkles is dead and she will be known from that point on as Robin Daggers. She then takes off her Robin Sparkles wig and jacket to reveal a darker look, and starts singing P.S. I Love You. The video further says that the one name that comes more than any other about who P.S. I Love You was about is Alan Thicke. Barney goes to his apartment to fight him, but returns with a black eye. Robin asks what happened to him and he tells her that they saw "Robin Sparkles: Underneath the Tunes" and that lead him to Alan Thicke who he fought. He tells him that "P.S. I Love You" song was not about him. Robin then says that it looks like he has become obsessed, which he realizes is true. He admits that anyone could become obsessed. Robin then tells them that P.S I Love was about P.S.; Paul Shaffer. She is sorry about scaring Paul Shaffer who was sitting in the front row of the Grey Cup, but she has no regrets as she was done being Robin Sparkles.
Meanwhile, Ted asks Jeanette if she pulled the fire alarm. She tells him that she was so close to meeting him, so she pulled the fire alarm as she couldn't stand the idea of not meeting him. Ted is charmed by this and tells Marshall and Lily that Jeanette is still a Dobler. Marshall and Lily later go to the university and see that there isn't even a fire alarm in the lobby and Jeanette must have started a fire to sound the alarm. Ted later asks Jeanette if she started a fire, and she says she did so to meet him, and Ted is charmed by this as well. Marshall keeps saying that what Jeanette did was not okay and asks Lily to support him. However, Lily says that she has been living a lie; back in Wesleyan, she saw Marshall at orientation. She made up the excuse of needing someone to set up her stereo and knocked at many doors before she found Marshall's room. However, Marshall is charmed by this. He apologizes to Ted and says that Jeanette is a Dobler and so is he.
Later, at his apartment, Ted tells Jeanette that if she hadn't been reading the same book as him, they would never have met and that's destiny. He then finds a receipt her book and realizes that she bought the book at the same store he did, within ten minutes of him buying his. She tells Ted that she followed him to the store. Ted asks how long she has been following him and she tells him a about year and a half ago, when he was on the cover of New York magazine. Future Ted then says, "Before a man meets the woman he will marry, he'll make one final horrible mistake. For me, that was Jeanette." Ted then starts making out with Jeanette.
Ted loves using yellow legal pads to help his thinking, as first seen in I'm Not That Guy.
Ted's legal pads are labeled "Property of Ted Mosby". His labeling is a recurring gag in The Over-Correction.
Jeanette claims to have been stalking Ted since he appeared on the cover of New York in The Best Man, a year and a half ago.
Barney refers to the fact he's one quarter Canadian while interviewing Robin's past ex boyfriends in the Vancouver Tim Hortons, which he learns in The Slutty Pumpkin Returns.
When past Lily walks through the halls in search of Marshall, she finds a girl wearing a "Vagitarian" shirt who she seems attracted to but walks away from, hinting at Lily's bisexuality.
Barney storms out of the Tim Hortons in Vancouver to search for the new Robin Sparkles music video immediately after hearing about it, like he did in the previous Robin Sparkles entry in the series. When he announces the discovery of "Robin Sparkles 4, y'all!", the gang rejoices as with the others.
Barney breaks into Robin's apartment using Ted's drill which Robin also used to break into his apartment in The Over-Correction.
Kids, sometimes, when you’re about to give up on your love life forever for the 17th time, destiny intervenes. (In the present, Ted is in the subway and sees Jeanette reading the same book as him) Instead of rushing in, I took my time to think of the perfect opening line. (As Ted is about to talk to her, she gets up and gets out of the subway)
Wait! No, damn it! Come back! You’re really… You’re pretty!
But here’s the thing about Ted Mosby: he doesn’t give up!
Stalker Ted alert! Repeat, stalker Ted alert! (Ted picks up a yellow legal pad)
Already has a yellow legal pad going! Repeat, already has a yellow legal pad going!
Look, there’s a fine line between love and insanity. It’s the Dobler-Dahmer theory. (Picks up a small legal pad)
Damn, I always forget the little one!
All right. If both people are into each other, a big romantic gesture works. Like Lloyd Dobler holding up the boom box outside Dianne Court’s window in Say Anything. But if one person isn’t into the other, the same gesture comes off serial-killer crazy, or Dahmer.
Hold on! I’m beginning to think that you guys didn’t come here to see my new lectern! Are you implying Jeanette started a fire?
Dobler! She’s John Cusack, I’m Ione Skye, and there’s nothing weird about that!
I'd fill up my journals all about him, and eventually there may have been a teensy-weensy 50-meter restraining order.
Fifty meters?! That's like... four years!
Simon Tremblay. I should have known!
Eh! Thanks for the free donuts!
They're just donuts, okay? They're like two for a loonie... dollar! What's happening?
She set a fire, Ted! Dahmer!
You’re just jealous ‘cause Lily never burned anything for you!
Clearly, you never tried her pot roast.
(in the Underneath the Tunes video) Who doesn’t love the mall? Shopping with your friends and… I can’t do this. Get this out of my face, please! Thank you. Pardon me. Thanks. Sorry!
Even when Canadians are mean, they’re polite!
It was tragic. I mean to this day, you ask any Canadian where they were when Robin Sparkles lost it, not only can they tell you which Tim Hortons they were in - but what donut they were eating. Me? Wawa, Ontario. Blueberry fritter.
Halifax, Nova Scotia. Walnut Crunch
Victoriaville, Quebec. Sour cream plain.
Sudbury, Ontario. Honey dip.
Red Deer, Alberta. Chocolate glaze.
Squamish, British Columbia. Crammed a Timbit into a strawberry vanilla and invented the Priestley. Should have been the best day of my life.
I am so happy right now.
I want to see her throw her life away so badly.
We're all terrible people turn it up.
—The gang is watching Underneath the tunes what is Canadian's behind the music special of Robin Sparkles.
Every guy that I'm with, I'll be thinking of you ♪
If I get married, he'll always be second to you ♪
That's got to feel good (Ted gives Barney a pat on the back).
—The gang is watching Robin Daggers video to try to figure who Robin's obsession was with.
That day is now known in music history as the day grunge was born.
In 1996, in Canada? That seems right, Trebek.
Give him a break, he's not a music guy.
That day is now known in music history as the day that grunge was born.
Well, that's a bummer.
They were right. You can't force destiny. If it's gonna happen, it's gonna happen. And funny story, kids.
—Ted is telling his kids about when he meets Jeanette.
Although she could have been lying so Barney wouldn't look for anything else, just like in every other Robin Sparkles episode, to avoid more embarrassments.
This makes sense since on their first trip to the Hoser Hut in Little Minnesota, Marshall sang Let's Go to The Mall and everyone knew the words and sang along.
This episode introduces some inconsistency in the story of how Lily and Marshall got together. In a flashback from Best Prom Ever, Lily is seen fixing the stereo in her dorm room while Marshall watches. In this scene she is talking about traveling the world and not having a boyfriend to tie her down, which would conflict with the idea that she broke the stereo on purpose to have an excuse to talk to Marshall and start dating him.
In False Positive, Alex Trebek is surprised when he states that Robin is Canadian, during the "interview" for the Coin Flip Bimbo for the show Heads or Tails. In the documentary it seems like he knows who Robin is and even states that the day Robin Sparkles turned into Robin Daggers, was the day the Grunge was born.
It’s possible that, due to the difference in looks, he didn’t recognise her.
In the flashback when Lily goes knocking on different doors to find Marshall, she has on black lipstick. But in the original flashback, she does not as can be seen when she finally finds Marshall.
Robin mentions that Paul Shaffer was at the game when she did her performance, and Jason Priestley claims to have heard Paul Shaffer's stomach churning, implying he was at the game too. Despite this, Priestley then claims he was at a Tim Horton's creating "The Priestley".
Priestley could have heard Paul Shaffer's stomach churning on the television screen.
Allusions and Outside References
MuchMusic is a Canadian music-television channel. Underneath the Tunes is a fictional documentary program that satirizes Behind the Music on VH1.
Everyone on the show keeps stating that the performance of the song was the birth of Grunge as a musical style, despite it having existed in America much earlier. This continues the joke about everything running on an approximately 15 year lag in Canada.
Everyone on the show mentioned where they were and what Tim Hortons doughnuts they were eating when Robin Sparkles unveiled herself as Robin Daggers. Alex Trebek said ate a honey-dipped doughnut in Sudbury, Ontario, which was the city he was actually born in.
His "cut it out" joke and accompanying hand gesture was a reference to his character's catchphrase in Full House which he starred in with Bob Saget. Future Ted's comment ("I've always liked that joke") refers to the fact that Saget does the voice of Future Ted.
In the full music video of "P.S. I Love You", there is a quick scene in which there are words written on a chalkboard that reads, "It's Paul Shaffer".
This is the last episode featuring Robin Sparkles. A scene was shot for the series finale of Robin in her denim jacket singing "Let's Go to the Mall" at the wedding reception, but this was cut due to time constraints.
Jeanette is the last woman Ted dates before meeting The Mother; Future Ted says she was "The last big mistake one man makes before meeting the woman he'll marry".
Hours after the episode aired, Tim Hortons announced on Twitter the creation of a new doughnut in response to a joke made by guest star Jason Priestley. The donut is known as "The Priestly".
This was the last episode in the entire series that coincided (i.e. air one day apart) with CBS' airing of the Super Bowl. Due to agreements that gave CBS the right to cover the game every three years, the network was also the Super Bowl's broadcaster in 2007 and 2010 when it also aired Monday Night Football and Rabbit or Duck, respectively. However, unlike in those two episodes, P.S. I Love You did not make any direct Super Bowl references although it spoke of a halftime show in the fictionalized version of the Grey Cup, Canada's counterpart of the Super Bowl.
Chuck Gerusi (Robin Sparkles' former agent) said that they booked the 1996 Grey Cup halftime show at the Ivor Wynne Stadium in Hamilton, ON, just outside of Guelph. Guelph is the hometown of one of the HIMYM writers.
Donna Bowman of The AV Club gave the episode an A-, calling it "a package that seems fresh and unforced despite an unprecedented heap of independently-filmed mini-segments and celebrity cameos." 
Max Nicholson of IGN gave the episode an 8.2 out of 10. He says that the episode was "easily the strongest episode of the season, thanks mostly to a bevy of cameos, a solid B story and Robin Sparkles' (likely) final appearance." He also said that the episode was "the first to deliver on every front, at least in some capacity, and I would definitely consider this a win for Season 8". 
Ethan Alter of Television Without Pity gave the episode a B-. He says that "If we could split the grades up, Underneath the Tunes would get a solid A, while the rest of the episode weighs in at a C+. So let’s give it a B- and call it a night, thankful that at least one aspect of this show hasn’t been completely desecrated.". 
The St. Petersburg Comic Review gave this episode 8 out of 10 stars. "...sometimes destiny happens..."