He seems to be running away from everything in his life.
The book opens with him going to visit his friend Dave, who has cancer.
He then proceeds to run way from Dave and join the Circus.
For the first half of the book Gary and Dave work as workmen on the circus. Until Gary gets tired of this and leaves to work on a high wire act. The rest of the book is just him and his high wire act. Then ending leaves a lot to be desired with the death of his dog and him avoiding circus life. Over all it was not a bad book. I however wouldn't recommend it to anyone.
"First-person narration by Gary alternate with vignettes told in other voices, a technique that produces a satisfying kaleidoscopic weave of perspective. The Aerialist is rich in behind-the-scenes circus lore and peopled with a large cast of unusual folk, but its greatest satisfaction lies in its informed literary authority." ~Amazon