In his novel, Shanower takes a traditionalist approach. With the exception of the villain, an old witch named Magda, he does not introduce new characters, but restricts himself to the original creations of L. Frank Baum.
Uncle Henry and Aunt Em have left Ozma's palace and the Emerald City to return to farming and the simple life. Dorothy comes to pay them a visit at their new farm in the Munchkin Country — when something goes terribly wrong: all of their vegetables grow to enormous size overnight, with gigantic beets, broccoli, peppers, and watermelons, and heads of cabbage twenty feet high. The farmhouse is hemmed in with a vegetable wall. Dorothy sets out for the capital for help, climbing a landscape of mountainous produce.
Outside the garden, Dorothy crosses the Munchkin Country and meets new friends, including a white and purple cow named Imogene, who gives varying dairy products depending upon her mood:
- "When I'm content I give regular plain old milk. When I'm thinking hard and get into a brown study I give chocolate milk. When I'm sad and blue I give skim milk. When I get excited, which doesn't happen often, I give butter. And when I get angry, sour cream."
In a crisis, Imogene can yield a healing golden milk; and in the course of the tale, she gives whipped cream and ice cream too.
Imogene talks Dorothy into accepting her companionship (the cow wants to see the Emerald City). With the help of the Wizard, Dorothy begins to unravel the mystery of the giant garden, and to follow the trail of a would-be witch called Old Magda who is its cause. The trio endure a thunderstorm and a near crash landing during a balloon flight. (Yes, cow in balloon.)
Magda created a giantism potion to make her garden more fruitful and her life easier — but lost control of it, resulting in giant moles eating giant vegetables. Dorothy falls victim to giantism herself and endures a subterranean ordeal (a surprisingly gritty and extreme adventure) before she, the Wizard, and Ozma resolve the problem and restore the normal order of Oz. Old Magda reforms, and Imogene gets her tour of the city.
Shanower gives his story a contemporary temporal setting, at the end of the twentieth century. Henry and Em have left the city "after eighty-some years of a life of luxury." The old couple are still fit enough for farm life, with some magical aids; people in Oz do not age unless they want to.
Other contemporary writers have taken the same approach: David Hulan sets The Glass Cat of Oz at the seventy-fifth anniversary of Betsy Bobbin's arrival in Oz, or the late twentieth century; Scott Dickerson sets The Magic Book of Oz at the centennial of Dorothy's first visit to the fairyland.