On the last day of a sea kayaking trip in southeast Alaska, fourteen-year-old Andy Galloway paddles away from his group to visit the nearby site where his archaeologist father died trying to solve the mystery of the first Americans. A sudden, violent storm blows Andy's kayak off course and washes him ashore on Admiralty Island, an immense wilderness known as the Fortress of the Bears. Struggling to survive, Andy encounters a dog running with wolves and then a man toting a stone-tipped spear. The wild man vanishes into the forest, but the dog reappears and leads Andy to a cave filled with Stone Age tools and weapons. Running for his life, Andy retreats deep into the cave, where danger, suspense, and discovery await.