Ernie is told to go to the store after school to keep an eye on it, but he disobeys orders and goes with Max to the Terra Dino Museum to sneak into a forbidden area still under construction.

Back in the present, Sue and Santiago discover their children's disappearances and learn that Tyra's real egg has switched places with the time machine.

Upon seeing an ancient carving on Mystery Rock, a local tourist attraction, which has been dated back to the Cretaceous, Sue realizes that spilling soda on the controls activates the time machine.

Back in the lower valley, the children run into the Sarco Brothers again and forgo their chance to return home to help Tyra, resulting in the time machine sinking into a tar pit.

When Sue and Santiago arrive in the lower valley, Tyra regains her strength and kills Sarco by pushing him into a tar pit.

Santiago reunites Tyra with her real baby before he and the humans return to the present, accidentally bringing home Dodger, who made the carving on Mystery Rock.

Additional voices by Melanie Abramoff, Jessica DiCicco, Benjamin Diskin, Dawnn Lewis, Megan Lovegren, Mary Elizabeth McGlynn, Jamie Simone, Roger Craig Smith, and Kari Wahlgren.