Giles is the main antagonist in the novel Cliffhanger. He is a big-mouthed brat and self-proclaimed leader of the Tigers.
During summer, Giles attends the adventure camp. He is one of the team called Tigers, along side with Tim, Biscuits, Kelly, Laura and Lesley. As soon as he arrives, he starts vaunts himself and his amazing sports skills and own, brand new sports equipment. He shares room with Tim and Biscuits, but doesn't like them, especially Tim who isn't good at any sports. After realizing Tim is a wimp, Giles throws his bag down of the bed, "accidentally" hits the boy with a tennis rocket and makes fun of his safety helmet. Luckily, Biscuits always upholds Tim and calls the bully "Piles".
Giles soon finds a rival in the camp - it is tomboyish Kelly who always wants to do everything first, just like Giles does, and the two often argue with each other. They both want to be a pitcher during the game of softball and they almost fall down from the cliff as fighting to be the first for rappelling.
During all activities, however, Giles always finds time to taunt and beat Tim, like for failing in softball and rappelling. Giles calls Tim mama's boy and considers many things in the camp to be "for children", although he brings his own teddy bear himself.
Much to Giles' anger, he is force to participate the canoe racing in the canoe with Kelly. However, it is soon revealed they are both very fast together and almost win the race, when Kelly's toy falls down into water. Tim and Biscuits save it, but the Tigers are defeated due this delay. During helping in the kitchen, annoyed Giles insults the two and Kelly, but he is then attacked by the rest of the Tigers who splash water on him.
The last activity, the Crazy Bucket Race, is very important for Giles who obsessively wants to win it. When Tim is sent to grass by a boy from the another team and it looks like they won't win thanks him, Giles gets really furious. However, when all teams eventually reach the stream, even Giles has no idea how to get on the second bank. Tim soon finds a solution, but Giles tells him to be silence. That is enough for the boy and Tim finally finds courage to answer the bully back and enforce his own idea. Thanks him, the Tigers win and Tim gets respect from everyone at the camp, even from Giles who becomes his new friend.