Magic Knight Rayearth I, Book One is the first volume of six in the Magic Knight Rayearth manga series.
The first volume opens up with three high school girls on a field trip to Tokyo Tower in where they are magically transported into the world of Cephiro. A land controlled by the will of those living in it and by the power of the one who acts as the pillar. The girls arrive and are suddenly confronted by a child looking mage called Clef who is much older than he looks, he explains to them the situation Cephiro is in and that they were called to the world by Princess Emeraude to become the Magic Knights and save Cephiro. The girls then travel to the forest of silence to meet with Presea who will create them the weapons they need to battle Zagato and revive the Rune Gods . First they must gather the needed minerals called Escudo to create the weapons which will allow them to evolve with the user. The first volume ends with the girls being saved from a large monster by a mysterious scarred man.
The adaption of this volume in the anime version is quite faithful it takes places in episodes 1, 2 and 3. There were only slight minor changes such as transforming Clef to stone, changing the appearance of Presea's hideout in the Forest of Silence and the fight against a monster.