Dragon Ball Z: The Book of Power is a non-canon feature film in the Dragon Ball Franchise. The plot takes place somewhat after the destruction of Majin Buu and before the encounter with Lord Beerus. The film follows the Unity Book, a powerful artifact discovered in the depths of the southern universe. With this book, users can be granted incredible abilities.
On a distant planet in the southern galaxy, a trio of assassin's break into the Royal Hall of Orkanos, a temple blessed by the kais. The assassin's swiftly take out the mightiest of guards and then proceed down to the Forbidden Pass. However, they are intervened by the Guardian of Orkanos. The leader of the assassin's steps forward. The two battle it out and the assassin destroys the Orkanos Guardian with a strong ki attack. The other assassins open the doors to the Forbidden Pass, and the three finally uncover the Unity Book.
Meanwhile, on King Kai's planet. King Kai watches the disturbance hast-fully. In his mind many thoughts are scattered. He says to himself that not even Lord Frieza was able to find the location of the Unity Book. He decides to call in the aid of Goku.
King Kai warns Goku of the book's extensive powers, saying that the Unity Book is capable of granting a power quite similar to the Super Saiyan transformation. Goku tells King Kai not to worry, and King Kai hands the co-ordinates out to him.
Goku teleports back to Earth, in search of Bulma. After a short conversation, Bulma decides to lend Goku her spaceship.
Goku, Vegeta, Piccolo, Gohan, Goten and Trunks board Bulma's ship and they are flown out to the destination.
Upon arriving on the planet, they are greeted by the Orkanos Guardian. The Guardian gives knowledge on the incident and where the thieves have gone. Goku tries to sense their energy and immediately spots an extremely high power level. The others grab hold of Goku whilst he uses Instant Transmission to transport to the location.
The assassin's are confronted by the Z-Fighters, and they engage in battle. The leader, Dablo defeats Super Saiyan Goku and Super Saiyan Vegeta almost instantly, and the other two assassins defeat the other z-fighters. Piccolo uses his extendable capabilities to retrieve the book from Dablo's inventory. Piccolo decides to open it, and is granted incredible powers.
Piccolo fights with Dablo, whilst the other Saiyans hastily recover. Goku transforms into a Super Saiyan 2 along-with Vegeta, whilst Mystic Gohan and Super Saiyan 3 Gotenks take on the other assassin. The assassin's finally reveal themselves as the strongest hit-men in the universe, and the book has allowed them to unlock their full capabilities.
Goku grapples the assassin, whilst Vegeta powers up a Final Flash attack. The attack succeeds, with Goku escaping the attack in the nick of time. Mystic Gohan and Gotenks defeat the other opponent, and they are left watching Piccolo's fight.
However, Piccolo is seen losing, as Dablo is gaining stronger from his race's capabilities. Suddenly, Vegeta is seen opening the book and is granted the book's power. Amazed with the results, Vegeta transforms into a Super Saiyan 3, and ascends further with the book. Vegeta confronts Dablo and destroys him.