Tyrone's lucky penny falls way down to the center of the Earth, and Professors Uniqua and Pablo use their inventions to try and help him retrieve it.
Tyrone is in the sandbox digging. He tells the viewer he is looking for his lucky penny, which must have fallen in the sandbox. Tyrone's search is interrupted by Uniqua pulling Pablo in a wagon. The wagon glides in the air after hitting the sandbox. Tyrone tells the two to stop because he needs to concentrate when looking for his lucky penny. Uniqua tells him that she and Pablo will help. They sing Amazing Inventors to explain how they are inventors who invent contraptions to make life easier.
The backyard transforms into a gray, two-story building on a London cobblestone street, where Uniqua and Pablo's inventions are on display. Uniqua points to a chart on a stand showing the Earth. Uniqua shows Tyrone an image of his lucky penny in the middle of the Earth image as Pablo explains how his penny probably fell to the center of the Earth. Uniqua and Pablo sing a reprise of Amazing Inventors as they show Tyrone their many inventions. They bring him to a room where a large metal drill is set up. Pablo tells Tyrone that it is their rocket-drill (which is part rocket, part drill), an invention they will use to get to the center of the Earth.
The three hop into the drill vehicle and sing To The Center Of The Earth as they start searching for the penny. Inventors Uniqua and Pablo stop the drill as Tyrone spots his penny on the edge of a spongy canyon. They all get out to retrieve it. Tyrone just wants to walk over and pick it up, but the inventors insist on using one of their inventions to retrieve the penny. Using a remote control, they operate a flying "grab-o-copter", carefully guiding it towards the penny. They attempt to get it with the grab-o-copter, but the claw attachment accidentally nicks the penny and it falls even further down to the center. Tyrone gets frustrated, then he and the two inventors return to the rocket drill and continue to go down. They sing a second reprise of To The Center Of The Earth, and when they finish, they drill down into a small cave of sliprock, which is extremely slippery.
They stop when they spot Tyrone's lucky penny atop a tall, diamond-shaped pillar. Tyrone puts the box of inventions on the ground and runs to the pillar, but Uniqua stops him and tells him again that they will use inventions to retrieve the penny. Uniqua gives Pablo shoes with toilet plungers on the bottom. She calls the invention "Vacuu-Shoes". Pablo uses the shoes to climb the pole and reach the penny. Tyrone asks Uniqua why they couldn't have just shaken the pole to get the penny, but Uniqua shushes him and replies that he'll break the professor's concentration. Pablo accidentally causes the penny to fall, and as it rolls around on the sliprock, the three dance and sing The Diamond Slide to the viewer as they try to catch the penny.
After the song, the penny falls into a small hole. The inventors and Tyrone get back in the drill and sing one final reprise of To The Center Of The Earth as they drill deeper. They reach a small island-like formation in the middle of a large, round moat. Pablo exclaims "We've reached the Center of the Earth!", as the three walk out of the rocket drill. Uniqua spots the penny in front of a large, green dinosaur. Afraid to walk over by the dinosaur to grab the penny, they use the inventions in the box to make an invention called the "extend-arm". Then, they sing a song about it, called The Extendo-Arm.
They try to use the arm to retrieve the penny, but the dinosaur notices and runs after them. They run for their lives to the rocket-drill, but the rocket-drill sinks into the water.Tyrone saves himself and his friends by playing 'fetch'. The dinosaur brings the penny back in his mouth and gives it to Tyrone. The three notice that the dinosaur is friendly.Tyrone invites the others to his house for sweet potato fries. The Center of the Earth transforms back into the backyard. Uniqua, Pablo, and Tyrone sing the end song, then they run into Tyrone's house. Tyrone opens the previously closed door and exclaims "My penny!".