The Queen of the Field Mice is a supporting character in L. Frank Baum's The Wonderful Wizard of Oz.
When the protagonist of the story named Dorothy Gale, her small pet dog called Toto and their three Ozian friends the Scarecrow, Tin Woodman and Cowardly Lion were on their way to the Emerald City to see the Wizard, they all past through a beautiful scarlet poppy meadow as they believed it to be a shortcut. But what they didn't know was that these poppies were dangerously poison and without being aware of this nor warned beforehand, they all walked into a death trap. And soon Dorothy, Toto and the Lion were put in a deep everlasting slumber when they came among too many of these mysteriously cursed flowers.
Since the Scarecrow and Tin Woodman were not made of flesh and blood like their other three comrades, the poison of the poppies did not effect them. Therefore when they saw their friends had fallen victim to these flowers, the two made it their mission to save the sleeping trio. Dorothy and Toto were light enough for the Strawman and Tinman to carry out of the poppy field; taken to safety and placed on a nearby meadow of rich green grass that helped the spell of the flowers wear off. The Lion however, (described as being nearly as large as a horse in size) was much too big and heavy to be carried out like the girl and her dog, so the Strawman and Tinman had to leave him behind to sleep on forever. All they could do was wish for their doomed friend to hopefully dream of finally finding his courage at last. Just as it seemed all hope was lost, a mean and hungry Wildcat ran past them and who was ruthlessly chasing a poor little mouse to make as its snack. The Tin Woodman saw this and out of compassion for the mouse, chopped off the Wildcat's head clean off with his handy axe to save the mouse.
The little cute mouse politely introduced herself as the Queen. And as a sincere thank you, she and her loyal mouse subjects were obliged to assist the two in anyway. The rodents lived in a nearby underground kingdom below the ground and because of their tiny size, the poison of the poppies did not effect them at all. So the rodents offered to help successfully rescue the Cowardly Lion from the sleep-inducing poppy fields. Later, the Queen and her subjects also were the ones to inform Dorothy that the Golden Cap had a magical charm that could be used to call upon the assistance of the Winged Monkeys after she defeated the Wicked Witch of the West. (The Wonderful Wizard of Oz)
In the sequel Oz books, she allowed a dozen of her subjects to go with the Scarecrow, who had been deposed as King of Oz, as part of his plan to regain the throne. (The Marvelous Land of Oz), published in 1904.