The episode opened with a Barney gag as we learned what the Cheerleader effect is. It's when a group of ugly women are gather together in a group that makes them hot as a group, but sled dogs as individuals. Very awesome. We then find out Barney might be a father!
Barney's not the only one with kids on his mind. Everywhere Lily and Marshall have been going there's been kids on their mind. When Marshall is ready to have kids, Lily seconds guesses herself and calls over her lawyers to please their cases, Ted on the pro side and Robin on the con. Turns out it doesn't matter because when Robin picks up her neighbor's baby's sock, she wants a baby.
An inebriated Lily goes to visit Marshall who's working late at the office to try and make a baby. However, after Marshall is forced to spend the night taking care of drunk "baby" Lily, he decides he's the one not ready for kids. However, when both Robin and Barney get a hold of the sock, they catch a little of the baby fever which leads to an awesome NPH rendition of Cat's in the Cradle.
Oh and did we mention Barney found out he wasn't a dad and formed his own holiday, "Not a Father's Day?" Oh and Robin moves into Ted's spare bedroom. Yay for awkward roommates!