When the castle of the knights of Gummadoon appears, Cavin is imprisoned as a spy. The Gummies only have until sunset to rescue him, as the castle only appears once every hundred years, but they also have to contend with Duke Igthorn, who plans to capture the castle.

Igthorn and his ogres have destroyed Gummi Glen, captured Dunwyn Kingdom and its citizens, and are keeping Grammi and Tummi held in Drekmore. Now Cavin and the remaining Gummies, with the help of the Barbics, must save them all while Zummi retrieves the Great Book and warn the Great Gummies to turn back.

King Gregor hosts King Jean-Claude, a ruler of a nearby Frankish kingdom, and his daughter Marie in order to improve diplomatic relations; but both Sunni and Calla learn that being a princess does not make one an instant sweet little girl. Even worse, Marie's haughty attitude eventually causes King Jean-Claude to stage a military siege on Dunwyn.

With no sign of Igthorn for an entire year, not even in his own castle, Zummi Gummi finds this news as a perfect opportunity to call on the Great Gummies (much to the skepticism of Gruffi). However, Igthorn has recently devised the ultimate plan to finally capture the Gummies, obtain the Gummiberry juice, and take over Dunwyn.

Tummi accidently causes a swarm of bugs to attack the gummiberry bushes.

Tummi learns through his new friend, the blind shepherd Trina, that handicapped people are not helpless.

Duke Igthorn catapults Toadie into the forest, where he accidentally makes his way into Gummi Glen and begins snooping around. When Tummi, who has been caught eating the other bears' picnic lunches and lying about it, sees him, no one believes him when he tries to tell them.

The Gummies find a Gummiscope, a gigantic machine that harnesses sunlight as a means of long-range communication, that could allow them to make contact with the Great Gummis across the ocean – but it can also be used as a weapon, causing Duke Igthorn to use it as a laser-type weapon to force King Gregor into surrender.

There is a thief in Gummi Glen, so Zummi and Grammi team up to find the rat. Unfortunately, Zummi casts the wrong spell which ends up shrinking them to a dimunative size, and they only have a limited amount of time to reverse it.

After an autumn of hard work and preparation for the coming winter, the Gummis are looking forward to the holiday of Fall's Farewell, but Sunni goes overboard with the celebration trying to impress Calla.

Tummi builds a full size boat, which Gruffi wants scuttled. However, out of respect for all the work done, he allows Tummi one sailing trip. This trip takes an unexpected turn when they end up on a volcanic island inhabited only by another Gummi Bear - an artist by the name of Gusto.

Sunni wants to find a new place to live but finds that Gummi Glen is the best home for a Gummi Bear.

King Gregor proposes a series of tests for Unwin and the other squires to become Princess Calla's bodyguard, which includes stealing a golden apple from the strong and mysterious Black Knight. Calla conceals her appearance in a suit of armor and competes as well to prove she is capable of her own self defense.

Eager to meet the Barbics, Cavin accompanies the Gummis on a trip to Ursalia. He is at first not welcomed by the Barbics, but soon gets the chance to prove himself in a manhood ritual which Buddy has to undergo in order to become a full member of his tribe. However, a pair of satyr poachers are on the prowl looking for furs to line their purses – and the Gummis just so happen to be quite hairy ...

Cavin becomes a great painter with a LOT of help from Gusto.

Igthorn comes into the possession of an invincible magical suit armor of an infamous villain from the past. Unfortunately, this armor fits diminutive Toadie only, and once the dwarfish Ogre realizes its power, he simply decides to take his Dukie's place as the ruler of Dunwyn!

When Lady Bane gets a lock of Sunni's hair, she uses it as part of a spell to keep her eternally young. Unfortunately, the spell also ages Sunni from a young Gummi to an old Gummi.

Grammi and Tummi go to feed a flock of giant birds just returning from their winter quarters, only to be forced to protect them from Igthorn hunting these birds to use them as war steeds and take care of one of their young at the same time!

Duke Igthorn sends a cursed gargoyle to King Gregor. The gargoyle comes alive at night and starts trying to destroy things – including the king himself.

Tummi has to clean up a big mess in Gummi Glen and bemoans that he is slow at the job. After tricking a tired Zummi into casting a spell on him, he learns that faster is not always more efficient when the spell proves unpredictable.

Sunni creates a growing potion while Toadie is cast out by Duke Igthorn. The two meet to unexpected results.

A ghost of a Gummi knight leads Cubbi on a quest.

Sir Gawain (Cavin's grandpa) tries to prove Gummies exist to win a bet.

Tummi takes pity on Doctor Dexter, an unsuccessfull pharmacist, and decides to improve his concocctions with a shot of Gummiberry juice. Unfortunately, this new wonder medicine also attracts the attention of Igthorn, and without the knowledge of how to exactly replicate the formula, the Doctor is caught between a rock and a hard place.

Grammi and Gruffi decide to trade their usual chores to find out who has the easier job. Meanwhile, Toadie and Igthorn discover blueprints for an ancient Gummi Bear logging machine, but needs a Gummi to build it for him, leading to another hunt for the bears.