Marco is the stepbrother of William Wagner, whom Allie Pennington believes is the reincarnation of Mordred. For a long time Marco singled out Miles as someone to bully. But every time he attempted to do so Will would intercede on Miles behalf.
During a party hosted by Will, Marco and some of his friends played a prank by planting a large fake bug on some of the food. When Will confronted him about it Marco and his friends left without incident.
On the night of the game Will disappears during the game. Marco went in search for him. Going to the school theater, Marco confronted Mr. Moore and was injured. Mr. Moore returns and reveals to Will, Allie and Miles that he is really Mordred and that Marco was actually a member of the Order of the Bear who was sworn to protect Arthur, and had been trying to gain Mr. Moore's trust. Mr. Moore then attacked the group. Allie grabbed a prop sword to stop Mr. Moore, but it transformed into Excalibur, revealing that she was the real reincarnation of King Arthur. Mr. Moore and Allie dueled in an alternate reality, where Marco, Will and Miles (Merlin) were also present and fighting. With the help of Merlin, Allie defeated Mordred.
Back in the theater the group are able to escape and Mr. Moore is detained. Marco knelt before Allie and pledge loyalty and fealty to her. Will then returns to the game and he proceeds to win the game.
Later, Marco and the others gathered together at the round table dressed as their legendary counterparts.