Barney's efforts to hook up with women are being thwarted by a mysterious woman from his past. Barney and the gang must sift though his many past flings in an attempt to find out who she is.

The gang learns a new way to get their dates to sleep with them after Ted walks in on Robin's date sitting naked on the couch.

When Barney learns Ted has a list of things he thinks the gang is too old to do, he sets out to do every task within 24 hours in order to prove Ted wrong.

When a perfect girl finally shows up, the gang tries everything to help Ted, while Marshall takes action when he discovers a letter written by younger himself.

Marshall and Lily try to figure out how to conceive a baby with the gender of their choice; Robin's perky new co-anchor irritates her.

When Marshall and Barney argue over the destruction of the Arcadian Hotel, Robin and Lily try to mix the right combination of cocktails that will force them to make up. Meanwhile, Ted plans a romantic weekend away with Zoey.

Robin receives bad news and decides to hide it from the gang. Marshall hangs Christmas decorations in his house in the suburbs with some help from his neighbor.