Morganna banishes King Arthur and the other knights by trapping them in ice. Merlin searches through time to find help in freeing the frozen knights. Merlin finds quarterback Arthur King, and his whole New York Knights football team and brings them to his time, The Medevil time.
Arthur must travel alone to Castle Morgana to save Guinevere and two of his imprisoned Knights (Lancelot and Trunk). Infiltrating the castle appears to be simple enough, but will he escape with his goals accomplished?
After welcoming a fleeing peasant into the sanctuary of Camelot, the peasant reveals to Arthur the location of one of the Keys of Truth which is known to reside within a church in the village of Wellton. However, Lady Elaine warns Arthur and his Knights of a premonition she recently has dreamt, foretelling the quest to gain the Key of Truth to be a trap.
Arthur has learned the location of one of the Keys of Truth - His own. Though getting out of Camelot to get the Key proves difficult, with the Warlord's blockade forcing Arthur and a small group of Knights to use Merlin's magical underground tunnel. Merlin is unaware that Morgana Le Faye uses her magic to discover exactly what the Knights of Justice are up to and so sets a trap near the tunnel's exit. Can this trap be sprung?
After enduring yet another siege attack on Camelot, Arthur decides that it is time to go on the counter offensive to rescue a Unicorn captured by Queen Morgana. The Unicorn is the key to finding all the Keys of Truth and whoever possesses the mystical creature will hold the advantage over their rival.
A magical being named Krisian comes to Camelot to inform Merlin that her father and Merlin's good friend Reicus is being held prisoner by a Sea Serpent. After Everett forces Arthur and his Knights to battle the Warlords, the Knights find help from a village and in fear of reprisal against the village, Arthur goes on alone with Krisian despite her warnings of a probable trap.
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.
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...
When Merlin is asked why Bog Lake is boiling, he learns that the key Lance can use to free Sir Lancelot is within. Tone creates a portable shed with scuba equipment of vines so Artur and Lance can search for it. The three, Wally, Brick, Breeze, and Lug avoid the Warlords on their way out thanks to a Merlin's decoy, but Morgana learns of the key about the same time the Warlords realize the trick. The Warlords attack just after an underwater chasm opens and the key falls in, and cut Lance's scuba so he topples in as well.
Despite Darren, Wally, and Brick fighting alongside him, Arthur is effected by Blinder in battle long enough for Hammer to wound him and Blackwing to steal Excalibur. Wally blames himself for not being able to protect him from every harm, so moodily avoids the others - then accuses the others of blaming him for their own failure. Then he defects to join Morgana, giving her Merlin's wand.
During a battle too early to tell which side is winning, the Warlords abruptly retreat when a lunar eclipse begins. Merlin remembers too late that it has transported the three attained Keys of Truth through an unspecified time in the twentieth century, which Morgana has told the Warlords. The portal is Grinlap's tree, so Arthur, Darren, and Tone return to time-travel again and reclaim the keys, but the Warlords are ahead of them. Annoyed by their confrontation in his home, Grinlap watches the Warlords go through the portal then throws the knights in.
Merlin dreams that he is attacked by the monster of Fear Island, the one place where his magic cannot function and where Tone's key is. He sends the Knights of Justice there with the warning that the creature's hideous appearance will disintegrate any who view it and they must use all their resources and wits to be the first to survive the isle.
