written by Dav Pilkey's fictional characters, George Beard and Harold Hutchins. It was released in North America on August 10th, 2010.
Ook and Gluk have been friends since they were babies. But they always take the spotlight away from Big Chief Goppernopper. One day Chief Goppernopper finds his throne defiled and takes this as the final straw. He and his guards go to their houses and sentences both of them to be arrested. Ook's sister Gak pleas to have mercy on them. Goppernopper falls in love with her and forces her to marry him against her will or else he send Ook and Gluk into the slammers.
Ook and Gluk try to think of a solution, but while walking through the forest they find Mog Mog. Eventually they are able to make Mog Mog fall into quicksand. They are at first happy with this until they see Lily. They realize Mog Mog was not bad at all. She just wanted to protect her baby. They try to get her out with a vine, but it doesn't work. They then go to a gorilla village and provoke one of the gorillas. The gorilla chases them until it knocks a tree down and grabs ahold of the boys. The knocked down tree gets Mog Mog out of the quicksand and she gets the gorilla's attention. This forces it to let the duo go and be nice to them before Mog Mog's roar scares it off. The duo along their with new friends go to stop the wedding before it's too late.
Elsewhere, the ceremony is underway and it appears to be going in Goppernopper's favor until Ook and Gluk arrive to object. Lily then goes and bites Goppernopper on the butt a few times until he yells out that he quits being their chief. He then takes his guards with him, vowing revenge on Ook and Gluk one day and says the same goes for Gak too.
After Ook, Gulk, and their little dinosaur pal Lily chase Chief Goppernopper and his guards away from the village, Chief Goppernopper stumbles upon workers from the future and his great great grandson. J.P. Goppernopper reveals that by the year 2222, all of Earth's natural resources have been used up. He and his workers have been stealing stuff from the caveman days with a time portal to substitute for the missing oil and trees as well as the polluted water and sell the stolen stuff for profit. Chief Goppernopper notes that he likes the reckless and irresponsible things that his descendant has done. JP asks Chief Goppernopper if he would like to work for him and Chief accepts. Chief asks if he would like some slaves as he knows where a whole village of cavepeople live and JP liking the idea agrees.
Back in Caveland, Ook, Gluk, Lily, and Mog-Mog are enjoying life without Chief Goppernopper around. They soon hear something approaching the village. Chief appears and declares the village the official property of Goppernopper Enterprises and the villagers are now the slaves of the enterprise. Chief then declares to the villagers to say goodbye to Mog Mog. The robo-dinosaur that Chief was riding on then beats up Mog Mog until she is knocked out. The cavepeople are then taken away to be Goppernopper Enterprises' slaves.
Ook and Gluk note that they both hate working. Chief then tells JP that Ook and Gluk are the kids he told them about. JP decides he has an idea for them. He then takes away the duo to his time. Lily frees herself and follows JP, Chief and Ook and Gluk to JP's time.
JP, Chief, and Chief's guards, have strapped Ook and Gluk onto a torture device. Before they can activate it, Lily bites the guards' toes as well as Chief's toes, allowing Lily to free Ook and Gluk and allowing all three to escape. the guards go after our heroes.
Eventually the duo and Lily hide in a garbage dumpster. The guards ask Master Wong if he saw two cowardly kids and a dinosaur run by. Master Wong states that is not cowardice, but a love of life. The guards don't understand this, but Master Wong falsely tells the guards the kids and Lily went somewhere else. After the guards leave, Master Wong allows Ook, Gluk, and Lily to stay and live in his school so they can hide from Goppernopper Enterprises.
At dinner time, Master Wong suggests to the cave kids that they should train and stay with his family until they are capable enough to defeat the corporation though the kids ask how as the corporation is big. Wong states that's only in a perspective. He gives a demonstration to the kids where they see Lily as small while a ladybug sees Lily as big and states that opposites can't be the same. After Wong finishes his speech on philosophy, Ook and Gluk find that hard on their brains and Wong's daughter, Lan states it can happen.
Ook starts to grow close to Lan, who gives Lily her official name as lilies are her favorites flowers. Ook and Gluk wish to learn to kick butt and use weapons, but Wong states that using violence and weapons to solve answers will usually never help and, after explaining that a peaceful man must never use normal tools as weapons, but use his body instead, he gives them two white belts as the start of their training. They become really good, though Lily's attempts to learn only end in her throwing up.
After a year, the cavekids want new belts as white belts are no longer cool to them. Master Wong states in order to get new belts, they must give the right answer to Master Wong's question: Who is the greatest man?. They ask if it's Wong and he states they are wrong. Throughout the years, no matter how good the kids become at kung-fu, Master Wong does not award them new belts as they constantly request as they don't answer his question correctly. Lily, on the other hand, remains small and still constantly throws up when she spins around.
When it is time for Ook and Gluk to save their village, they finally answer who the greatest man is: nobody. It is the correct answer to Master Wong's question, so he finally awards them black belts, telling them that titles and trophies have no value to the man who is at peace with himself and true greatness is anonymous, therefore the greatest man is literally nobody. Ook and Gluk realize that these belts have no value since they are at peace, but they take the belts anyway.
Then Ook, Gluk, and Lily enter Goppernopper Enterprises and defeat Chief Goppernopper's guards and break in. JP sees the intruders via security cameras and, upon recognizing them, sends his robots after them. Ook and Gluk are quickly beaten and captured, but Lily saves them by getting herself to throw up near the robots, causing them to slip and break as well as free her friends. JP gets mad at our heroes' interference, but Lily, who is still dizzy, unintentionally thows up into JP's mouth, which distracts him long enough for Ook, Gluk and Lily to use the time portal to go back to the cavemen days.
Upon arriving, our heroes, defeat the guards and free the slaves. Then Ook's sister Gak falls in love with Gluk and calls him a hero. After that, Chief Goppernopper returns and orders his Mechasaurs (A mechanical Tyranosaurus, a mechanical Triceratops, and a mechanical Pteranodon) to attack Ook, Gluk, and Lily. The Mechasaurs chase our heroes back into the future until they hide in a warehouse and wear some paper bags to hide themselves.
When the cavemen discover the robots will destroy anything that has Ook, Gluk, and/or Lily's faces on them after using spray-paint on a building, Lily and the cavemen spray-paint pictures of themselves on the buildings so the Mechasaurs will destroy all the buildings owned by Goppernopper Enterprises. They also spray-paint on the Goppernopper Enterprises building so it will be destroyed, and spray-paint on the explosive tank, which also destroys the Mechasaurs themselves.
After Ook and Gluk's victory, J.P. Goppernopper sends them a letter, telling them that he captured Master Wong and Lan and that they will be killed to death if Ook and Gluk won't give up now. When Ook, Gluk, and Lily return to 2222, they see Master Wong and Lan tied up. As soon as the Goppernoppers are going to kill the Wongs, Ook and Gluk pleads with the Goppernoppers to release the Wongs and say they will do anything. The Goppernoppers agree and have Ook, Gluk, and Lily handcuffed and change their minds about releasing the Wongs and vow to kill them all.
Ook and Gluk wonder how to get out of this and Master Wong tells them to remember their training. Then Ook and Gluk remember all of the teachings from Master Wong and get an idea. When J.P. Goppernopper raises his ray gun to kill them, Ook and Gluk ask the Goppernoppers the question: Who is the greatest man? J.P. Goppernopper answers that he is the greatest man while Chief Goppernopper answers he is the greatest man. After that, the Goppernoppers disagree with each other and argue about who the greatest man is and get into a fight. J.P. Goppernopper betrays and zaps Chief Goppernopper, killing him and accidentally erasing himself from history, as Goppernopper did not have children yet.
The polluted world begins to be replaced with the world without Goppernoppers. Ook, Gluk, and Lily run back to the disappearing time portal, but Ook soon returns because of his love for Lan. Lan says she will be his cave-wife and they both enter the cavemen days.
The time portal, at this point, now fully disappears. Master Wong walks home where he says there is a part of the kids in him. A sign shows Ook and Gluk's future descendants open a business right next to Master Wong's Kung-Fu School called "Shadowski & Jones Inventors".
Lily finally re-unites with her mother Mog-Mog. Ook, Gluk, Lan, Mog-Mog, and Lily return happily to Caveland.