Goby and Gil go on a quest to get a geode at the top of a volcano. They try to make it back to the Rocky Valley Rock Show in time to enter the contest for best rock.
The episode starts with Goby showing off his rock, the other guppies and Mr.Grouper are amazed by his discovery. Mr. Grouper then decides to put Goby's rock in the school's rock collection. The kids are stunned by the unique rocks. There is even one made from a volcano. Mr.Grouper then asks the audience about what rocks are. The guppies then sing a song about rocks.
In Rocky Valley, Goby, Gil, and Bubble Puppy set on a quest to find the coolest rock to complete his rock collection and showcase off at the Rock Show. Goby then decides to find a geode, a rock that contains crystals inside. However, they are very hard to find and the only place to find them is near a volcano. Yikes! Nevertheless, they are still thrilled to find one. The boys then get help from Deema to find a volcano, after finding one Deema warns them about dinosaurs.
Now on their way to find a geode, Gil is scared about encountering dinosaurs. Goby and Gil are having trouble finding the rock. Geodes are round in shape and you have to crack them to find the crystals. The guppies then met up with Oona and Zooli for lunchtime. Zooli then shows pictures of geodes to Goby which are located on the top of the volcano. Gil then stumbles upon an unusual geode which is a dinosaur egg. The egg then hatches which is revealed to be a baby T-rex. The Momma T-rex worried about her daughter, roars in distress which scares off Goby and Gil. Oona and Zooli then take a picture of them.
The roars from the Momma T-rex made the guppies closer to the top of the volcano. Goby having a hard reaching the geodes asks Gil for help. After getting the geode, the volcano erupts! Luckily, the trio makes it out alive but the baby T-Rex is in danger! The Momma T-rex then finds her baby but the lava is in the way. Gil and Goby then solve a puzzle so that the mother can rescue her baby. The mother thanks the kids and takes them to the Rock Show.
After they arrived, Goby shows off his rock but the audience is not impressed. Goby then realizes he has to crack the rock but has trouble doing so. The Momma T-rex crushes the rock with her foot, opening the geode The audience applauds Goby and he wins the rock contest and a party is thrown at the end.