Twelve year old Goku seeks out Master Roshi to ask to be accepted as a student just before Krillin, a monk from a far off city, arrives for the same reason (and uses a Dirty Magazine as a bribe). Master Roshi sends them on a quest far to the west, where "five mountains stand, called the 'Devil's Hand'." In a castle there, there lies the legendary, and beautiful, "Sleeping Princess." Whoever brings back the Sleeping Princess will become the old pervert's student. The two boys set out, and Krillin uses all the standard tricks to trip Goku up.
A little later, Bulma, Oolong, Yamcha, and Puar, who are on summer vacation, arrive at Kame House to find Goku. Master Roshi says that the two boys have gone far to the east for training, so the friends fly in Bulma's Capsule jet to the Devil's Hand. When they near the castle, the jet is attacked by demons, and Bulma is taken to the castle. The owner of the castle, Lucifer, pretends to treat her as a guest, until it becomes time to awaken the Sleeping Princess. In the meantime, Goku and Krillin fight monsters, and Yamcha drops in on Bulma just before the butler Igor can drain Bulma of her blood through a giant syringe (Bulma's blood is to be used to toast the awakening of the Sleeping Princess). Then, Launch (in her bad, blonde state) arrives to steal the Sleeping Princess, which is really a giant jewel. Everyone is captured and encased in a wall of rock.
It is the night of a full moon, and the moonlight is used to power the jewel (the full-moonlight is to be used to destroy the Sun and begin the Reign of Darkness). The moonlight also turns Goku into a Great Ape, who then goes beserk and grabs Good Launch. Great Ape Goku's tail is cut by Yamcha and Puar, which reverts him to his base form, and everyone then escapes. They find and fight Lucifer, and Goku uses a Kamehameha to move the Devil Castle Cannon towards Lucifer, and it kills Lucifer. The heroes escape, and Krillin acts contrite, but does not actually apologize to Goku for his behavior.
The two boys return to Kame House with good Launch and Master Roshi, mistaking Launch for the princess, takes them both on as students. Roshi tries to take advantage of Good Launch only for her to sneeze and attack him with her gun before sneezing again.