Baboon finds a baby in a cornfield and decides to take care of him, and adopts him. Baboon's neighbor, the Red Guy from Cow and Chicken (!), sees all this and mentions that something like that just isn't natural. (S)he calls for the super nanny, I Am Weasel to come and take care of the baby instead of Baboon.
Weasel arrives, in a similar fashion as Marry Poppins does, and starts teaching Baboon how to take care of his baby. Lots of funny scenes and memorable quotes follow, and the conclusion is that Weasel finally learns that Baboon does indeed love his baby and decides to let him keep his baby.
Fast forward to the future, where we see the baby all grown-up (oddly enough, he's the only one who aged...) and the Red Guy is once again beaten up by SuperCow! He even mentions that he wasn't expecting SuperCow would find him in an I Am Weasel episode.
So, pretty much this episode brings us the first Red Guy appearance in an I Am Weasel episode. His addition is an welcomed one, as the following episodes will become better than the ones from the first season.