Holden was the final person to be added to the gang after Maya. After he arrived, Kate explained to him how she and Star were abducted by whitecoats while on a school field trip and experimented on, leading to them acquiring their abilities.
Later, as the gang was beginning to play Never Have I Ever, he said that he didn't know how to play. Fang explained how to everyone, and everyone got in a circle, after which the game began. During the game, Holden said that he's never owned a designer bag, which agitated Star; and (untruthfully) that he's never had his finger grow back after chopping it off.
While at the San Diego Comic-Con, Holden said that it was going to be awesome after seeing a group of cosplaying girls walk by. He also gave Fang an idea on how the Doomsday Group would manage to hold their rally.
Holden called Ratchet's enhanced hearing "so cool" after he managed to hear something from a mile away. As the gang was about to enter the rally at SDCC, a boy thanked them for coming, to which Holden said, "You're welcome."
The rally eventually brought the crowd to a fever pitch, causing Holden to notice the physical alterations of the people in it.
After the rally, he asked if the Doomsday Group members could be arrested for what they were doing.
Holden breathed fire as part of a public entertainment display—Fang's successful attempt to get the gang and the Flock invited to the Doomsday Group's rally in Paris, France. At one point, he took a swig of flammable liquid and burped out his ABCs.
Later on, as Angel told everyone her plan to spy on the Doomsday Group while in their hotel room, Holden suggested an older kid do the work. This causes some controversy, and Max eventually tells him that Angel will be alright, causing him to stop talking.
During the riot, Mark repeatedly shot Holden, but the kid's healing abilities caused the bullet holes to close up in seconds.
Holden eventually left with the gang after Fang said they'd be separating again.
Holden was first seen staring at Star after she ate an entire omelette in a single bite. Eventually she made a remark about how Maya was the next generation of Max, causing Holden to say, "Ouch," and whistle.
Later, the gang got on the road and Star got in a fight with Ratchet, which resulted in giggles from Kate and Holden.
After the gang's van was hit by Ari's truck, Holden was described as having assumed a battle stance.
During the fight with Ari and his companions, Holden's arm was torn into by an Eraser, though Fang saved the kid from death. After confronting Star briefly, Fang went to find him and saw his wounds healing before their eyes.
After another confrontation with Kate and Star, Fang announced that the gang was splitting up. Holden's fate afterwards was unknown until several months later.
Maximum Ride Forever
Holden somehow survived the apocalypse and joined Angel's army. A short time before the battle with Dr. Hans Gunther-Hagen's army, Holden was seen playing soccer with a group of buglike mutants. They supposedly had contests over who had weirder skin. He helped Iggy and Gazzy work on a catapult and fought with the bug boys during the battle; after Dylan's death, he and Kate were the first to respond to Max's screams.
He was described as a thin, pale, and scrawny kid with lots of scars on his arms from when the whitecoats ran tests on him. In Nevermore, he was said to have "sandy"-colored hair. He was also said to look about 10 years old even though he was almost 15, which led to teasing from the gang.
In Nevermore, Holden was described as being the most awkward member of the gang.
Holden can breathe underwater and has the regenerative powers of a starfish; therefore, he was nicknamed Starfish. It was also said that one of his other skills is the ability to annoy Star.