Phineas and Isabella gets trapped

In this episode, while building a tunnel to the center of the earth, Phineas falls in! Isabella jumps in to save him, but failing. The two of them land in a strange world full of thinks that could kill them. They end up getting trapped in a spickey plant. After a few hours of being together, Ferb and The Fireside Girls come to save them and everything comes back to normal.