How I Met Your Mother: 10 Biggest Unanswered Questions
7. What Happened To Abby?
Abby was introduced in the show's third season as Stella's receptionist. In her first appearance, she falls deeply in love with Ted, only to be rejected when he starts seeing Stella. She then hooks up with Barney, despite her enduring feelings for her boss's boyfriend.
After her fling with Barney, Abby disappeared for a while, only to return with a vendetta against the infamous womaniser, which sees her following him around New York and ruining his chances at various one-night stands.
In her final appearance, she puts all that aside and teams up with Barney to try and make Ted feel bad for his and Barney's recent falling out. At the end of the episode, Barney gives Abby Ted's address, and tells her to go after him once and fall all. The episode closes with her deviously smiling at the address.
But then she vanishes. Abby's never seen or heard from again. Given the cliffhanger, and Britney Spears' hilarious performance, it's a shame we didn't get more time with her, but it sucks more that we were never told why or what - if anything - happened.