Timmy and Stitch: The Big Beginning is Part 1 of 3 of the "Timmy and Stitch" trilogy.
In Part 1 of 3, Stitch from "Lilo and Stitch" comes to Dimmsdale to meet Timmy and all of his friends, Lilo, Jumba, Pleakey, Nani and all the experiments. Timmy meets each experiments and meets Gantu too. Then Jumba introduces Timmy all of his experiments. But then Stitch is kidnapped by Gantu and Lilo must save him.
One day Timmy is playing ball with his dad until he hears a wheesh in the winds. It is an airplane. There Timmy sees a surprise. It's the "Lilo and Stitch" characters and Timmy sees them. Then Jumba introduces the expermints Timmy meets. The experimints are also friendly to him. Then Lilo meets Timmy and says "Aloha". Timmy becomes great friends with Lilo. They have a fun time. Meanwhile all the expermints want to introduce to everyone in the world. And then Gantu comes to Dimmsdale too and starts to find all the experminits and kidnaps Stitch to Anti Fairy World and Timmy and Lilo are angry that Gantu took Stitch. Now that Gantu kidnapped him, he calls Vicky for kidnapping and thinks it's a dog but it's an alien. So Vicky comes along with Stitch. In Anti Fairy World the Anti Fairies hear a knock on the door and Gantu comes in. Then they lock Stitch in Foop's room. The Anti Fairies, Gantu and Vicky come up with a plan. They make a evil twin of Stitch called Anti Stitch. He decides to ruin everybody's lives.