Cubbi wants to play knight, but when the Gummies don't believe Cubbi sees the ghost of a real Gummi Knight, Cubbi sets out to learn from him and help him fulfill an unfinished quest.
On a peaceful day in Gummi Glen, Cubbi suddenly barges into the main hall wearing a bucket and wielding his wooden sword and shouting about an Ogre attack. The others momentarily panic and prepare to defend the glen. But, when Cubbi begins to taunt and attack a suit of Gummi armor, they realize, much to their annoyance, that Cubbi is pretending to be a knight and the attack was a false alarm.
Sunni scoffs at Cubbi's aspirations to be a knight, but Cubbi defends himself, reminding Sunni that he is an honorary knight of both Dunwyn and Gummadoon. Grammi chides Cubbi that real knights are courteous and helpful and don't go around causing trouble. She then asks him to go the forest to fetch stinkweed, which he reluctantly agrees to.
While wandering the forest and lamenting how he should be off on an exciting quest, Cubbi stumbles upon a large stone monument covered in vines and underbrush. It is adorned with a proud-looking statue of a gummi knight and bears an inscription which reads, Here Lies A Great And Noble Night Sir Gallant. Cubbi stares at the statue in awe and wonders if he will be honored like this great Gummi hero one day, when he is Sir Cubbi.
Just then, a voice calls out from nowhere, and the ghost of a Gummi Knight appears before Cubbi. Cubbi flees in fear, returning to the Glen and knocking into the others as he slides down the escape chute into the main hall. The ghost follows Cubbi into the glen, and Cubbi tries to defend himself, but it becomes apparent that Cubbi is the only one who can see or hear him. Cubbi runs to his bed, hiding under the covers.
Some time later, the others, now more annoyed than before, come to confront Cubbi about his behavior. He mentions the ghost, but they do not believe him and Grammi warns him against telling any more stories. Just as they leave, the ghost reappears and explains that the reason the other's can't see him is that he can only be seen by a true Gummi knight. He reveals that he is Sir Gallant, the knight whose memorial Cubbi had found, and that he needs help from a true Gummi knight to complete his quest.
Sir Gallant explains that when he was alive, his quest was to destroy the fearsome Doomsday Clock, a dreaded weapon built long ago by an ancient wizard with the power to destroy the world in the wrong hands. Sir Gallant reveals that his spirit cannot rest until the clock is destroyed. Cubbi, broken out of his fear at the prospect of a real quest, eagerly agrees to help.
Later, the two are out in search of the clock, with Sir Gallant revealing that the ancient Gummi compass he wears around his neck will glow brighter as they get nearer to their target. Along the way, Cubbi's learns what it means to be a true knight. He almost runs headlong over a land bridge overlooking a huge gorge, only to learn that the bridge will collapse with the slightest pressure. Later, he tries to use his Gummiberry juice to bounce up a mountain, but Sir Gallant forbids him from doing so, stating that a Gummi knight must learn to rely on himself.
After a long climb, the two reach a mesa at the top of the mountain. Cubbi, exhausted and disillusioned that the life of a knight is not all glamour and glory, complains about their journey to Sir Gallant, just as a piece of his shirt falls loose, having been torn in the climb. Sir Gallant gives Cubbi a sewing needle and thread, chiding the young Gummi that a knight can't go around looking like a vagabond. However, Cubbi is frustrated at being corrected and neglects to sew the tear completely. Instead, he carelessly pins the tear back in place with the needle.
Further up the mesa, Sir Gallant reveals the clock is close at hand, but there is nothing in sight. Cubbi grows frustrated that they have come a long way for nothing, but suddenly steps on a hidden trapdoor and rides an elevator hundreds of feet into the earth. When he finally stops, he looks up to see a cave full of gold, treasure chests and other riches. At its center is the Doomsday Clock, and Sir Gallant is relieved to see it hasn't been set in motion yet. Sir Gallant hands Cubbi a wrench reveals that Cubbi must dismantle the clock's golden gears to destroy it. Just as Cubbi approaches the clock, a voice is heard from behind them and a troll runs at Cubbi, accusing him of stealing the treasure. Cubbi explains that he is not there for the treasure, but to save the world. The troll does not believe him, but instead of apprehending Cubbi, shoves past him and heads for the clock, breaking Cubbi's juice bottle in the process.
Cubbi gives chase and the two struggle to reach the clock first. During their scuffle however, they accidentally knock over a treasure chest which bounces into the clock's pendulum, setting it in motion. Sir Gallant reveals that if the clock's hands reach midnight, the world is doomed, and the clock is now at 11:55 and counting down. The troll again tries to defend the clock, but Sir Gallant chases the him away with his sword while Cubbi begins to climb into the clock. Unfortunately, the clock is huge and the golden gears lie five stories on top of a labyrinth of other clockwork.
After a great deal of climbing, Cubbi finally reaches the golden gears and starts to dismantle them, when the sewing needle holding up the rip in his clothes falls out, and his torn shirt catches in another gear, pulling him back and preventing him from using his wrench. Cubbi momentarily panics, lamenting that he should have listened to Sir Gallant and fixed his clothes properly. Fortunately, this gives him an idea and he jams the needle between two of the gears, and the clockwork begins to fall apart around him. He barely makes it out in time before the clock explodes, and is met by Sir Gallant and the Troll. The troll is thankful that Cubbi saved the rest of his treasure, but becomes hysterical with love for his gold pieces, and Cubbi and Sir Gallant quietly leave.
Back at the monument, Sir Gallant thanks Cubbi and gives him the Gummi Compass as a token of his gratitude and disappears, hailing Cubbi as the last of the great Gummi knights. Cubbi returns to the Glen and gathers the group together to tell them about his adventure, but they still do not believe him, thinking he is still pretending. Gruffi then notices the compass and asks Cubbi where he got it, but Cubbi walks away, defeated, saying that Gruffi wouldn't believe him if he told. Just as he does so, the compass glows, and Sir Gallant can faintly be heard giving his catchprase, "Excelsior!"
- Goofy Holler: As Sir Gallant chases the troll away with his sword, the troll can be heard in the distance letting out the Goofy holler.
- The Doomsday Clock in this episode is based on the real symbol of world catastrophe that has been maintained since 1947 by the members of the Bulletin of Atomic Scientists.