Season 1

1. Chapter 1 "The Old Grist Mill"

Two half-brothers, Wirt and Greg, and an unnamed frog are lost in a forest called the Unknown. They meet a woodsman chopping trees, who warns them of "The Beast" who preys on lost wanderers like them. He offers to help and takes them to an old grist mill for shelter. They are followed to the mill by a fearsome creature, which the brothers take to be the Beast. Greg knocks out the Woodsman, and the two brothers attempt to fight "the beast", destroying the mill in the process. "The beast" coughs up a turtle it had swallowed and reverts back to a calm domesticated dog.

Upon waking, the Woodsman is angry that the mill was destroyed. He chastises Wirt that he needs to take responsibility for himself and his younger brother. He warns them that the Beast is still at large, and advises the brothers to seek shelter in a nearby town, and give the frog a proper name.

2. Chapter 2 "Hard Times at the Huskin' Bee"

Wirt, Greg, and the frog travel to the town of Pottsfield. Along the way, they "rescue" a talking bluebird, Beatrice, from a thorn bush. In return, Beatrice offers to guide them to Adelaide, "the good woman of the woods", who can help them get home. In Pottsfield, they find the residents celebrating a harvest festival, all dressed from head to toe in pumpkins and straw. The brothers are cautioned that they might be in Pottsfield "too early". Enoch, the village leader, charges them with trespassing and disturbing the peace, sentencing them to a few hours of manual labor.

The brothers end up assisting with the harvest. As they dig holes in a field outside the village, Wirt becomes afraid the Pottsfield residents plan to actually kill them and bury them there. Instead, skeletons emerge from the graves they dug, dress themselves in pumpkins, and are warmly welcomed by the community. Wirt realizes that all of the Pottsfield residents must be skeletons. As they are allowed to leave Pottsfield, Enoch tells Wirt, "You'll join us one day." The brothers follow Beatrice to Adelaide.

3. Chapter 3 "Schooltown Follies"

Wirt, Greg, Beatrice, and the frog come across a primary school with animals as students. The human teacher, Miss Langtree, mistakes Wirt for a student. All she teaches them is about how the man who was courting her left her. Greg plays outside with other animals until they all retreat into the school to escape a gorilla. At mealtime, Greg tries to cheer everyone up by singing and adding molasses to their bland mashed potatoes. The meal is interrupted by Miss Langtree's father, the school's founder. He confiscates their musical instruments and sends them all to bed.

In the night, Greg and Wirt sneak out and find Mr. Langtree camping in the woods. They hear him lament that he will have to sell the instruments to continue funding the school. When Mr. Langtree wakes, he finds Greg and Wirt have organized a benefit concert, which raises enough money to keep the school open. The gorilla appears again and Wirt trips and falls into it, revealing that the gorilla is Miss Langtree's missing beau wearing a costume, having joined the circus to earn money for an engagement ring.

4. Chapter 4 "Songs of the Dark Lantern"

Wirt, Greg, Beatrice, and the frog visit a tavern to ask for directions to Adelaide's house, but Beatrice is forced to wait outside after the tavern keeper throws her out, believing that bluebirds bring bad luck. The people in the tavern warn the brothers about the Beast, telling them that the creature turns people into trees of oil to burn in his lantern. Based on this description, Wirt concludes that the Woodsman must be the Beast. Hearing Beatrice in distress, Wirt steals a talking horse named Fred and rides to her rescue.

He finds Beatrice unconscious next to the Woodsman. Wirt and Greg fend off the Woodsman and ride off with Beatrice. A shadowy figure appears to the Woodsman and reminds him to be careful, that the flame inside his lantern contains his daughter's soul, and that he must cut down Edelwood trees so the fire can keep her alive.

5. Chapter 5 "Mad Love"

The brothers pose as the nephews of the wealthy and eccentric Quincy Endicott so they can steal two cents from him to pay for the ferry to get to Adelaide's house. Endicott tells them he has fallen in love with a ghost he saw one night, but fears he is going insane. While Wirt and Beatrice search for pennies, Endicott takes Greg and Fred to search for the ghost. Beatrice reveals to Wirt that she was once human, but she and her family were cursed by a bluebird and Adelaide is the only one who can change them back.

Wirt reveals he has a crush on a girl back home named Sara. They discover that the ghost is not a ghost but Endicott's business competitor, Margueritte Grey. They conclude that both of their mansions are so large that they are connected. They admit their love for each other and, thankful for his help for introducing them, each award Greg a penny. However, Greg discards the two cents in Quincy's fountain, claiming that he has "no cents, no cents at all". Fred stays with the two lovers as an official tea horse.

6. Chapter 6 "Lullaby in Frogland"

Without two cents to pay, they have to sneak aboard the ferry. All the other passengers and crew of the ferry are frogs dressed in fine clothing. Greg feels bad because his frog is nude. They disguise themselves as members of the ferry's band. With encouragement from Beatrice, Wirt reluctantly plays the bassoon as Greg's frog unexpectedly starts to sing, and they succeed in maintaining their cover. When they arrive at their destination, Beatrice, who has been acting strangely throughout the ferry ride, tries to convince them to stay in the Unknown and not to visit Adelaide.

That night, Beatrice flies away to Adelaide's house. Wirt and Greg follow her in secret. The brothers learn that Beatrice originally planned to give them both to Adelaide as servants in exchange for a pair of scissors that would lift the curse from herself and her family. Adelaide attempts to capture Wirt and Greg, but is killed by Beatrice. Beatrice tries to explain that she had a change of heart, but Wirt and Greg are already gone.

7. Chapter 7 "The Ringing of the Bell"

Wirt, Greg, and their frog come across an isolated cottage. Inside, they meet a girl named Lorna, who hurriedly hides the brothers in a basket full of turtles from her caregiver Auntie Whispers. Auntie Whispers uses a magic bell to control Lorna and makes her work constantly lest she "become wicked"; she also darkly warns that unwelcome visitors to her cottage will be devoured. The brothers try to help Lorna escape by helping her finish her housework early. Just before they leave, Greg and his frog accidentally awaken Auntie Whispers, who warns them to stay away from Lorna or they will be "gobbled up".

While they are hiding from Auntie Whispers, a horrific demon possessing Lorna's body tries to eat them. Greg reveals that his frog has eaten Auntie Whispers' bell. Wirt uses the bell inside the frog to command the demon to leave Lorna's body and never return. Lorna, now free, decides to stay with Auntie Whispers. As a final farewell, Auntie Whispers warns them to beware of her sister Adelaide. Wirt begins to lose hope of ever leaving the Unknown, which pleases the Beast, who is watching from afar.

8. Chapter 8 "Babes in the Wood"

The brothers and frog sail down a lake, where they hear the Beast's singing, and Greg remains hopeful while Wirt has given up. They reach land and sleep under a tree for the night. Greg dreams of being welcomed by the residents of an angelic cloud city. The festivities are cut short when the North Wind is released and starts terrorizing the city. Greg defeats the North Wind by trapping it in a bottle. The Queen of the Clouds appears to Greg, allowing him one wish as a reward. He wishes to find the way home, but the Queen tells Greg that Wirt is too far gone and is covered in Edelwood branches, signaling that the Beast has claimed him.

Greg instead wishes to take Wirt's place, and leaves with the Beast. Wirt awakens to find snow falling and Greg gone. He tries to chase after them, but falls into a frozen lake, only to be rescued by Beatrice.

9. Chapter 9 "Into the Unknown"

In a flashback to Halloween before the brothers get lost in the Unknown, Wirt makes a cassette tape for his crush, Sara. Greg gives the tape to Sara's friends, who put it in her jacket pocket. They tell Wirt that another boy, Jason Funderberker, intends to ask Sara out at a party. Desperate to get the tape back without embarrassing himself, Wirt follows Sara to the party and then to the graveyard for ghost stories, oblivious to the fact that Sara is delighted to see him and has no interest in Jason.

A police officer jokingly scolds the teens for being in the graveyard. They scatter, and Wirt and Greg climb up an old stone wall. From the top, Wirt sees Sara finding the tape, and he panics. They jump off down from the wall, landing on train tracks. As Greg finds a frog in the bushes, a train approaches. The brothers jump out of the way and fall into a lake. They sink, both unconscious. In the present, Wirt wakes up and finds himself with Beatrice's bluebird family. He thanks them and heads off into a snowstorm to look for his brother.

10. Chapter 10 "The Unknown"

While Greg performs meaningless tasks for the Beast, Beatrice finds Wirt. As Greg transforms into an Edelwood tree, the Beast attempts to persuade the woodsman to use Greg as fuel for his lantern. When Wirt and Beatrice arrive, they try to free Greg from the tree; Wirt names Greg's frog "Jason Funderburker". The Beast offers to preserve Greg's soul in the lantern, if Wirt takes over the responsibility of keeping the lantern lit. Wirt is tempted to accept this offer, but realizes that it is actually the Beast's soul that is in the lantern.

Wirt frees Greg from the branches, gives Beatrice Adelaide's scissors, and finally gives the Woodsman the lantern. As Wirt and Greg leave, the Woodsman extinguishes the lantern. Wirt wakes up in the lake, back home, and pulls Greg and his frog to the surface. The brothers are taken to the hospital. Wirt wakes up surrounded by Greg, Sara, and her friends, and invites Sara to listen to the tape at his house together. The frog's stomach glows with Lorna's bell still inside. Back in the Unknown, the Woodsman finds his daughter alive, and Beatrice and her family have been restored to human form.