An extra-terrestrial mad scientist named Dr. Jumba Jookiba is imprisoned for illegally experimenting and creating creatures to cause chaos and destruction. His latest experiment is Number 626: a cute, little, blue alien with four arms, two legs and antennae and three spines from his back who is deceptively strong, fast, intelligent, destructive and indestructible.
Captain Gantu, a shark-like alien, is assigned to take 626 to a penal colony, but during the trip, 626 manages to escape in a smaller spacecraft, and crash lands on the small Hawaiian island of Kaua'i, on Earth. Masquerading as a dog, 626 is adopted by a little girl named Lilo Pelekai who is living with her 21-year-old sister Nani after their parents died in a car accident. Lilo is lonely and a bit of an outcast until she finds a new friend in 626, whom she names "Stitch." Stitch initially attempts to escape the island but finds that it is impossible because he is afraid of the water and cannot swim because his body is too dense. Stitch resigns himself to stay with Lilo when he spots that he is being watched by Jumba and Galactic Agent Pleakley, who have been assigned to recapture Stitch without being detected by humans. Lilo notes Stitch's violent tendencies and attempts to teach him to relax.