This book tells the story of The Secret of the Sword from the point when He-man is imprisoned by Hordak and his energy is being drained by power the magnabeam. As for a summary of the book's content:

"The Princess Of Power" is basically the second half of the book "The Sword Of She-ra". In this half, we get a brief two page summary of what has happend so far: Adam has traveled to Etheria to find the sword's owner. When he learns that the Evil Horde rules Etheria, he decides to become He-man. Eventually, He-Man finds Force Captain Adora, who learns that she is the Princess of Eternia, and that she is He-man's sister. At this point, Adora becomes She-ra for the first time.

In part 2, He-man's energy is being drained to power the Magna Beam and She-ra intends to rescue him. After She-ra tosses He-man his power sword, He-man regains his strength and the two try to escape from the Fright Zone and stop the Magna Beam from activating and destroying the Whispering Woods. As She-ra prepares to take on the Magna Beam, she discovers that the Power Of Grayskull transforms her horse Spirit into Swift Wind, a talking unicorn with colorfull wings. She-ra takes advantage of her horse's new flying ability and quickly intercepts the Magna Beam's ray with a gigantic boulder. Siezing the oppertunity She-ra created for him, He-man smashes the Magna Beam with his incredible strenght. The instant the machine is crushed, the prisoners Hordak had drained to help fill the Magna Beam's power source regained their strength.

Victorious, He-man and She-ra flee to Whispering Woods, where they learn the secret of their past. The Sorceress tells He-man and She-ra all about how Adora was kidnapped as a baby by the evil Hordak. Eager to meet the family she has never known, Adora returns to Eternia with her brother. The siblings travel to the Royal Palace, where Adora finally meets her Mother and Father.

Angered by the loss of Force Captain Adora, Hordak travels to Eternia to apprehend his former slave. Upon retrning to Eternia, Hordak is confronted by his old pupil Skeletor. The two trade blows until an agreement is met; Skeletor and his allies will aide Hordak in re-capturing Adora.

Back at the palace, Skeletor's men overpower the royal guards and take Adora prisoner. When Adora is taken to Snake Mountain, Hordak prepares a dementional gate that will take both Adora and himself back to Etheria. Unfortunatley for Hordak, Skeletor has decided to keep the princess for himself. Skeletor quickly pushes Hordak into the portal and has Adora put in the dungeon.

After being locked in the dungeon, Adora pretends to faint. Beastman and Tri-Klops, the two henchmen who are supposed to be keeping watch over the princess, are fooled by Adora's clever deception. She is able to incapacatate her guards and get her sword back. After Adora transforms into She-ra, she escapes from Snake Mountain and returns to the palace where she informs her family that she's going to fight for the Great Rebellion back on Etheria instead of staying on Eternia.

When She-ra returns to Etheria, she and the Great Rebellion decide to re-take Castle Bright Moon from the Horde. Assisting the rebellion on this mission is none other than He-man, who could not let his sister face the Horde alone.

After Castle Brightmoon is taken back by the rebels, Hordak flees and He-man prepares to return home.