Arthur Pendragon arrives from Avalon in London. There, he breaks into Westminster Abbey looking for the Stone of Destiny (also known as the Stone of Scone) hoping to find Excalibur, but Excalibur has not returned to the stone.
He is accosted by Griff, gargoyle guardian on London, but is able to explain himself. The Stone speaks and says it will take King Arthur to Excalibur if he can speak its location. Griff recites a riddle he learned about Excalibur as a hatchling.
Isle of towers, glass and stone,
The Lady waits for him alone,
Ebon glass in emerald frame,
Pure white lilies speak her name,
Blood red bane in dragons stone,
Excalibur waits for him alone.
When Arthur speaks the first line, he is transported with Griff to Manhattan. When they arrive, Macbeth is waiting for them. As Arthur does battle with Macbeth, Hudson, Brooklyn, Lexington and Broadway arrive and chase Macbeth away.
Brooklyn is able to help Arthur with the next part of the riddle and he finds and awakens the Lady of the Lake. She tests him with a water creature. When the creature is destroyed, she gives him the next clue.
Meanwhile, Macbeth overhears the clue. He sends his henchmen to delay Arthur and the Gargoyles while he seeks the sword in the maze for himself.
Brooklyn and the others battle Macbeth's henchmen while Griff and Arthur search through the maze.
Macbeth arrives at the center of the maze first and pulls the sword from the stone dragon. When he does, the stone dragon awakens. Macbeth, Arthur and Griff do battle with the stone dragon. During the battle, Macbeth drops Excalibur and Arthur retrieves it. As he holds it, he realizes it isn't Excalibur at all, and breaks the blade.
The stone dragon captures Macbeth and Arthur and flies off with Griff hanging on.
The Manhattan gargoyles finish with Macbeth's minions as the dragon takes flight and they follow, doing battle in the air. As Arthur struggles in the grip of the dragon, he understands the last piece of the riddle. Calling for Griff's help, he frees himself and then breaks the blood red stone in the dragon's chest, freeing Excalibur and destroying the stone dragon.
On the ground, Macbeth acknowledges Arthur as the rightful wielder of Excalibur and pledges his help should Arthur ever need it.
Back at the clock tower, Arthur says he will stay through the day, but when night comes he must begin his search for Merlin. Griff asks to accompany him.