The guys go to a coffee shop, where Ted points out that Chloe (Morena Baccarin), the girl working there, has drawn a heart next to Marshall's name on his cup. Ted insists that Chloe has a crush on Marshall because she always laughs at his lame joke about how they fit a pumpkin into a pumpkin-flavored latte. As Marshall leaves, his name is called for (an unordered) pumpkin latte on which Chloe has written her number. Later, when Marshall introduces Chloe to Ted and Barney at the bar, they tell him that she has the "Crazy Eyes", an indicator of future mental instability. Both Ted and Barney give Marshall examples of their experiences with this malady; Barney's crazy-eyed date wanted a threesome with a teddy bear, while Ted's crazy-eyed date picked up a long metal rod and repeatedly hit a car that nearly hit them as they were about to cross the street. Marshall shrugs it off. The next day, as Marshall is taking a test, he receives a call from Chloe who says that she is being followed by a hunchback with a limp. Later, Marshall takes Chloe back to his apartment and suspects that she broke a picture of him and Lily that was sitting on the end table. However, it turns out that Lily has been hiding in the apartment, and pops out (much to Marshall and Chloe's surprise). Lily introduces herself, and leaves the apartment dejected and crying. Marshall follows her out to the steps, leaving Chloe sitting on the sofa.
Lily confides in Robin that she is scared by the idea of Marshall going out on a date with another woman. Despite hearing that Ted believes she has crazy eyes, Lily wants to see what Chloe looks like. It turns out that Lily was the hunchback following Chloe—she was carrying a book bag, then covered herself with a coat to shield herself from the rain (the hump), and limped because she hit her knee while concentrating on seeing the face of Chloe. Lily, while visiting Ted and Robin in the apartment, realized that Marshall had moved the picture of the two of them. She sneaked into the apartment before Marshall brings Chloe home to put it in a more conspicuous place, and it broke. While hiding from Marshall and Chloe, she got upset and popped out.
Marshall realizes that he should get back together with Lily even though he says that Lily has the craziest eyes he's ever seen. Six months after Ted came back to the apartment and found Marshall alone and upset after the engagement ended, he returns to find Marshall and Lily happy and back together. The gang first goes to McLaren's for a drink and then returns upstairs to the apartment, finding it has been ransacked by Chloe who has been "searching" for her "lost" keys which are in fact sitting in plain sight on the coffee table in front of where she had been sitting. Marshall points out the keys and Chloe departs, leaving a nonplussed gang and apparently proving the "Crazy Eyes" theory.
Meanwhile, Chloe writes Barney's name as "Swarley," prompting everyone to call him the name for the duration of the episode. Barney protests, but variations on the nickname become a running gag throughout the episode. Just prior to leaving the apartment, Chloe calls Robin "Roland", and Barney tries to use it as an opportunity to stop everyone from calling him "Swarley". In the final scene, however, Barney walks into the bar, everyone shouts "Swarley", and he turns and walks out dejectedly as Carl the bartender plays "Where Everybody Knows Your Name."