Tom the Cat and Jerry the Mouse get whisked away into The land of Oz.
In Kansas, a farm girl named Dorothy Gale lives with her Aunt Em and Uncle Henry, their three farm workers are Zeke, Hickory, and Hunk. She has a pet cat and mouse named Tom and Jerry. Tom and Jerry's rivalry, however, often gets in the way of their work. But the duo prove to be useful when they manage to save Dorothy when she falls into a pig pen. Aunt Em persuades them to put their rivalry aside and work on protecting Dorothy from harm.When a neighbor, Miss Almira Gulch, is bitten by Dorothy's pet dog, Toto (although it was her own foul temper that provoked Toto in the first place), she gets a sheriff's order and takes him away to be put down. Tom and Jerry give chase on an old bicycle. Jerry manages to free Toto, who runs back home, but Tom and Jerry end up in a scuffle with Miss Gulch which culminates in the three of them crashing into a pit. Tom and Jerry return home without helping Miss Gulch, just as a twister reaches Dorothy's farm. Dorothy, Toto, Tom and Jerry are too late to join Dorothy's family in the storm cellar, and Tom and Jerry are knocked out as they try to get inside the house.
Once they awaken, they find themselves in a strange village. As they wander around, they encounter a grey Munchkin mouse, Tuffy, who tries to protect Jerry from Tom, assuming he wanted to eat him, but Jerry clears up the misunderstanding. Tuffy informs them that a few hours ago, the house they and Dorothy arrived in landed on and crushed the Wicked Witch of the East, and as gratitude, the Good Witch of the North, Glinda, gave Dorothy the witch's Ruby slippers, but the Wicked Witch of the West appeared and swore to claim the slippers for herself. Glinda sent Dorothy down the Yellow Brick Road to reach the Emerald City and find the famed Wizard of Oz in order to get back home. Though Tuffy advises them not to follow Dorothy, Tom and Jerry remember their promise to protect her and insist on following her. Tuffy decides to accompany them so that he can wish to become taller.
Eventually they come to a crossroads in a cornfield, where two crows point them in the direction Dorothy went with the Scarecrow that was previously perched there. Unfortunately, it turns out that the crows pointed them in the wrong direction by accident. Tom, Jerry and Tuffy come to a particularly worn and dangerous part of the road by a mountain and across an old bridge, where Tom more than once nearly falls to his death. Along the way, they come across the Witch and hide in a giant dandelion while the Witch observes Dorothy and her three friends, the Scarecrow, the Tin Man and the Cowardly Lion, from a cliff with two of her Flying Monkeys. Tom, frightened by the Witch's resemblance to Miss Gulch, accidentally sneezes, which prompts the Witch to turn the dandelions into an avalanche. Tom, Jerry and Tuffy attempt to get the wand from the Witch and end up in a scuffle with her before Jerry manages to turn the boulders back into dandelions, saving Dorothy and her friends from death, and sends the Witch away, but the wand disintegrates into sand. Vowing revenge, the Witch flies towards the Emerald City.
Tom and Jerry reunite with Dorothy and meet up with the Scarecrow, Tin Man and Lion, who respectively claim that they want to wish for a brain, a heart and courage from the Wizard. They finally reach the Emerald City, where they are looked after to recover. Tom comically tries to eat someone's pet chick, but Jerry and Tuffy stop him by submitting him to a painful massaging machine. The Witch then appears and demands that they surrender Dorothy, Tom and Jerry. Tom tries to hide, but Jerry and Tuffy find him and remind him of the promise they made. Reluctantly, Tom remains with them, but they are refused entry to the Wizard's chamber, where the Wizard is speaking with Dorothy. They come outside and tell them that the Wizard will not grant them anything unless they bring him the Witch's broomstick.
On their way to the Witch's castle, Dorothy, Toto, and Tom and Jerry are captured by flying monkeys, but Tom and Jerry manage to get free before they reach the castle. They climb up the castle to the tower, where they see the Witch threatening Dorothy over the ruby slippers and placing Toto inside a basket. Jerry valiantly manages to free Toto, who runs off to get help, but is seen by the Witch and thrown through the window with Tom. They land on a lower level and encounter the Witch's two top guards, Droopy and Butch, who casually mention the Witch's one weakness being water. A long chase ensues until Tom and Jerry manage to knock Droopy and Butch out, and they reunite with Tuffy, the Scarecrow, Tin Man and the Lion, disguised as guards and led there by Toto. As the others find and rescue Dorothy, Tom and Jerry fill a bucket of water to use on the Witch, but their attempts to get it back into the castle fail due to comical circumstances. Eventually, Tom and Jerry manage to get hold of a rogue rain cloud and use it to fill the bucket. Finally, the Witch and her men corner Dorothy and her friends inside the vestibule, and the Witch sets the Scarecrow on fire. Jerry rushes to their aid with the bucket of water, but trips over and drops it, although it doesn't spill. Dorothy frantically uses the water to put out the fire, and splashes the Witch in the process, causing her to melt and die. To their relief, the soldiers celebrate the Witch's death and allow Dorothy to take the broom.
They return to Emerald City and present the broom to the Wizard. But he refuses to grant their wishes. Although the Wizard turns out to be an ordinary man behind an illusion and a humbug, he nevertheless promises to grant their wishes and take Dorothy, Tom and Jerry back to Kansas on his hot air balloon. But as the balloon takes off, Tom spots the chick and sneaks out to eat it, prompting Jerry and Toto to follow him to stop him. Dorothy runs after them and they are unable to get back to the balloon before it takes off. Glinda then appears and tells her another way to get back home, by tapping her heels together and repeating "There's no place like home". Dorothy bids farewell to her friends and follows Glinda's instructions.
Dorothy, Tom and Jerry awaken in Dorothy's bedroom back in Kansas, surrounded by family and friends. Dorothy tells them of her adventures, but they insist it was all a dream, though Tom and Jerry are the only ones who believe her. As Dorothy promises never to run away again, the same old habit did not change while Tom swipes Jerry with the broom continually outside the house during their chase, much to the amusement of Dorothy and the others.
