Marcus Warwick, also known as Boy 410 in the Young Army, is twin to Matt Marwick and Mandy Warwick (Wolf Boy). His father was a Guard in the Castle who was convicted as a traitor shortly before the death of Queen Cerys. Marcus and his brothers spent their childhood in the Army until it was disbanded. He was close to Matt, but it is unknown how well they got along with Boy 409, or how they reacted when he fell off the boat and was thought to be dead.
Sometime after his Young Army days, Marcus and Matt were employed at Gothyk Grotto. Mr. Igor, the owner, always called Marcus Matt and vice versa because he thought the boys switched names. Marcus met Beetle in Dan's Dive while taking a shortcut to work. He helped Beetle look for Jenna, but they were unsuccessful.
Marcus was safe during the Darke Domain because he stayed in a SafeChamber at Gothyk Grotto with his brother, boss, and new co-worker, Marissa the witch.