The Land of Oz is situated somewhere within the fairy realm. It can be accessed from Earth through the use of a special key, that once used on any door, turns it into an entrance to Oz. The only other method of entry into Oz is through natural disasters, like tornadoes, the eye of a hurricane or whirlpools. Time also moves differently in Oz, as Dorothy was still in her 20s in 1935, despite The Wonderful World of Oz being published in 1900. Clive Dillon also appeared to be in his 50s in 2014, when he should be well over 100 years old.
L. Frank Baum who was a member of the Men of Letters traveled on a case and his daughter Dorothy snuck along with him. Dorothy got trapped in Oz and fought the Wicked Witch of the West. The Witch is extremely powerful and has armies of witches and flying monkeys fighting for her. Dorothy fought alongside three freedom fighters who were later cursed by her to become the Scarecrow, Tin Man and Cowardly Lion. The Tin Man and Dorothy both died during the adventures, but while Dorothy was resurrected, the Tin Man was not and Dorothy kept his head to honor him.
After the Wicked Witch came to Earth, L. Frank Baum wrote the books based on Dorothy's adventures to give her clues on how to deal with the Witch. The Wicked Witch tried to find the key that was in the possession of the Men of Letters, which opens a portal to Oz, so that she could complete her war.
After the Witch was killed in 2013 by Charlie Bradbury, Dorothy and Charlie returned to the realm to free it from the Wicked Witch's forces and to find Dorothy's dog Toto. A war was fought and was eventually won after Charlie made a deal with the Wizard of Oz to split herself into her good and dark halves. Dark Charlie single-handedly won the war and Dorothy and the Wizard became the new leaders of Oz, while Charlie chased her dark self back to Earth to stop her. Unknown to Dorothy, the Wizard was evil and was just using her to gain power. With the help of Clive Dillon, the Wizard was summoned to Earth where Charlie killed him by killing Clive, his good half. With the Wizard dead, Oz was presumably finally free of evil influences.