When King Arthur and the Knights of the Round Table are defeated by the Warlords and then Queen Guinevere is later captured by the foes, the wizard Merlin recruits a group of football players (and their equipment manager) from the present day to protect Camelot and save the queen.

Having repelled the Warlords once, the Knights of Justice continue to make their way with Merlin's help toward where Morgana holds Guinevere. Morgana is aware that King Arthur and his knights are still imprisoned so those approaching are strangers. She succeeds in capturing Lance and Trunk, causing Arthur to travel to her castle to rescue them as well.

Lady Elaine warns Arthur and his Knights of a premonition she recently has dreamed, foretelling the quest to gain the Key of Truth to be a trap.

Merlin's falcon reveals to him that the key Arthur alone can use to free King Arthur from the Cave of Glass has been found. Merlin creates an impenetrable tunnel to send Arthur, Gallup, and Phil most of the way to retrieve it, but Morgana is aware of the extreme use of magic so reasons whom has used it and why. She sends Lord Viper and the Warlords to Crownhorn, the village it's ended up near, just after the knights stand up for Orin, a villager in a misunderstanding with an army of gnomes then are offered hospitality by him and his wife Kate. Suspecting the knights are in the home of Orin or a neighbor, they kidnap Kate with orders for Orin to bring a knight to him to ransom her.

The Warlords make a failed attempt on Camelot, though do cause a fire. Lug is having self-esteem issues since he fears the dangers faced in battle and is still equipment manager, just in a different time and leading squires as well. Lord Viper and Blackwing succeed in capturing a unicorn for Morgana that she may use its power over all animals to beat the knights to finding the Keys of Truth. Merlin learns of this when the balance of magic is out of order as a result, and sees it as a cure for the restlessness of most of the knights. He sends Arthur, Breeze, Wally, Trunk, and Lug to free it, but they accidentally end up taking along Tyronne, who fell asleep in Arthur's wagon.

The magician Cryslin requests Arthur's help in freeing her father, King Arthur's sorcerer friend Rigis, from a sea serpent. He accepts and goes with Lance, Tone, Breeze, Trunk, Gallup, and Everett, but Everett's falling off the wagon she turned invisible reveals them soon after. The Warlords attack the knights near a village where a group of boys assist them in the victory. But the men in the village fear the Warlords, who vow vengeance on them. The knights stay behind to defend it against their promised attack while Arthur, despite learning from Crislin that she was leading him into a trap in exchange for her father's life, goes with her anyway to defeat the serpent and rescue Rigis.

Lance and Breeze are attacked by Warlords on their way back to Camelot from a mission, and Lucan succeeds in forcing Lance off a high cliff. While the Knights of Justice try to get over the shock of his loss, the Warlords learn he is actually alive but with amnesia when he approaches them. They take him to Morgana, who realizes that his tumble into the River of Forgetfulness will let them trick him into thinking he is one of them. They claim he is the Warlord Sir William, twin to Lancelot who just defected from King Arthur, whom she convinces him is evil, Everyone is overjoyed when Lance returns to Camelot, but don't know that his surprisingly distant behavior masks that he intends to deliver them into Morgana's hands.

Breeze is wounded during a battle with the Warlords. Determined to let none of the other Knights of Justice come to harm at his side, Arthur challenges Viper to single combat, and has Zeke deliver it with other Warlords as witnesses so he'll have to keep his word. But everyone else's misgivings about Arthur's plan prove well-founded when Viper employs treachery in the duel.

Tone builds a hang-glider for Arthur, Lance, Darren and Trunk to invade Castle Morgana.

Merlin dreams that Viper possesses a Key of Truth and defeats Darren, and concludes that Darren's key is in Morgana's and the Warlords' domain. Tone builds a hang-glider for Arthur, Lance, Darren, and Trunk to invade Castle Morgana, but Darren falls into the castle grounds and is captured. Morgana intends to use a machine to unleash a potion which will turn him into a Warlord himself, then, learning how many others must still be nearby looking for him, do the same to them. The other knights are fighting more than time through her danger-infested castle to reach him and the key first.

Arthur and Breeze are attacked by the reincarnation of Viper.

Tone and Merlin share a dream that, during a battle, Tone falls through a tree and finds himself in a hospital where he sees his mother in a coma which it's believed his presence could help her recover from. Merlin realizes it was a true vision since he had another of the same tree, the new location of the Key of Truth for King Arthur - which can actually be used along with another to transport the knights home, if briefly. But the tree is inhabited by the giant Grinlap. Arthur, Tone, and Darren with his own key set out to retrieve it so Tone can see his mother awaken, but the Warlords don't intend to let them have another key...