Justin is a five-year-old boy introduced partway through Lies, being described as an older child in Mary's daycare who still wets the bed. When Justin goes back to his house he finds Roger, (known as the Artful Roger) who had been staying in his house. Roger and Justin became roommates. In the fire, their house burns down, injuring Roger and forcing Justin to drag him out.
Later on in Lies, when Mary is about to jump off the cliff, Justin tries to deny her but she holds his hand and doesn't let him go. He falls off the cliff but is saved by Brianna.
In Fear, Justin is living at Lake Tramonto, on a houseboat with Roger, Diana and some other children. He hasn't got a particularly large role until Drake emerges from hiding underneath the boat, kidnapping Diana to deliver to the Gaiaphage and using Justin to force Diana to come with him. Diana agrees and saves Justin's life, but dooms him to accompany Drake on his way to the mineshaft. When they arrive in the ghost town, Brianna emerges, trying to stop Drake from getting into the mineshaft. However Penny appears and unites with Drake, ruining Brianna's attempt to kill Drake by making her see visions of lava all over the ground. The four then head into the mineshaft away from Brianna just as the dome turns dark. Sometime in their journey down into the mineshaft, Justin is forgotten and left behind near the big drop, until Brianna finds him on her way to defeating Drake. Justin warns her about the drop and she leaves him there, telling him to wait for her return. When Brianna comes back from her encounter with the Gaiaphage she leads Justin out of the tunnel and he was returned to safety.
In, Light, Justin is killed by Gaia when she attacks Lake Tramonto and incinerates everything, using Sam's power. Justin is among the approximately 70 other residents, around a quarter of the entire population of the FAYZ, who die in that single attack.