The arrival of Stillwater's niece Koo has Karl feeling a bit unseen. Addy puts on a show with her brothers but needs to learn to collaborate.

Karl is disappointed his gem museum doesn't attract more visitors. Addy's time with her classmates gets disrupted by Karl's antics.

Michael feels overwhelmed by how long it'll take to build his dream treehouse. Karl copes with the loss of his favorite climbing tree.

Karl is upset that MuMu, his favorite stuffed toy, is “broken.” Addy feels betrayed when her best friend spends time with someone else.

Karl and Koo think of ways to make their playdate last forever. Stillwater is anxious about everything he has to do before his trip.

Stillwater shows the kids his worm farm and other things he does to live green, which inspires them to come up with more ways to help Earth.