Role in the film
Gavin is first seen with a group of lumberjacks cutting down some trees in a forbidden area of the forest; much against his boss and brother, Jack and his brother's fiancée, Ranger Grace Meacham's wishes. After hearing his niece, Natalie screaming due to falling from a tree and hurting her leg after pursuing a boy named Pete she spotted in the woods earlier, Gavin arrives and manages to catch Pete while unintentionally rendering him unconscious as he tries to escape.
After Jack, Natalie, and Grace leave with Pete to take both children to the hospital, Gavin and his men notice some trees falling their way to the ground, thus, arousing his suspicions that something is hiding in these woods and decides to go hunting. At night, after a long search, Gavin and three of his men finally find Pete's tree house along with his possessions in the cave including his favorite book, "Elliott Gets Lost"; knowing Pete couldn't have lived on his own or built this house by himself, which later enrages an invisible force that fully reveals itself to be Pete's dragon guardian and friend, Elliott. Shocked and scared at the sight of it and its roaring, Gavin and his men run for their lives as Elliott chases them away. Once they reach their truck, Elliott stops them from driving further away. When Gavin aims to shoot Elliott with his shotgun, Elliott manages to turn invisible again, swipe the gun from his hands, and break it into pieces as he throws Gavin to the ground. Then, Elliott ironically sneezes on him, leaving him covered in spit and mucus and continues to drive away with his men back to town.
When he arrives at his brother's home and tells him what he saw, he is mad and disappointed to see that his own brother doesn't believe him and decides to take matters in his own hands. The next day, he goes out into the woods with some more men to search and capture Elliott alive. While Elliott is getting acquainted with Pete's new friends: Natalie, Grace, and her father, Mr. Meacham, Gavin and his men take this opportunity to ambush Elliott by tranquilizing him with sleeping darts and capturing him in ropes despite Elliott's resistance; much to Pete and his friends' horror and shock including Jack, who came just in time to witness what has happened.
Then, Gavin and his men bring back Elliott wrapped up in chains on a truck to their warehouse where he intends to show the dragon to everyone including the sheriff and the police and become immensely rich. His actions, however, don't gain him the respect of his family and that of Pete or Mr. Meacham at all. Once the police arrive, Gavin tries to show the sheriff the dragon but finds the door to the place he is being kept in locked from the inside, therefore, knowing that someone is inside (Natalie and Pete). Once they finally get the door open, they find the place to be "empty"; thinking the dragon managed to fly up to the open roof after someone freed him when in fact, he is still here (completely invisible). Later, seeing that someone is driving the chain free, yet still weakened dragon out of the warehouse and back into the woods, Gavin tries to pursue them even though Grace tries to delay him by throwing his truck keys away.
During the chase, Gavin catches up with the truck carrying Elliott only to find Mr. Meacham, Pete, and Natalie driving it. After they refuse to listen to Gavin's objections, Gavin decides to drive straight ahead of them and block them with his truck on a nearby bridge. However, due to faulty brakes, Mr. Meacham is still able to drive straight for them, which causes them to move out of the way and lose their truck down the ravine. Then, Gavin watches Elliott, now fully-strengthened, trying to stop the police from chasing him by breathing fire on the bridge. His fire, however, causes the bridge to collapse. Realizing that Jack and Grace are unable to avoid the collapse due to having unintentionally driven on the bridge, Elliott manages to save them even after they have all fallen into the ravine; much to everyone's joy including Gavin's. After that, Gavin gives up on Elliott's capture and decides to move on.