There could be many instances deemed as the most important events in the book. For me, it would have to be when Bruno hops the fence to accompany Shmuel to find his father. It is important because it represents the first time that both boys, in separate worlds, find themselves converged in the same one. It is also significant because it is the first real instant where we see Bruno's heroism. He is scared by what he sees and experiences, and yet does not acquiesce because of the promise he made to Shmuel. Naturally, it is because he crossed over the fence that his death is almost inevitable. When they are rounded up into the gas chamber, Bruno holds Shmuel's hand and comforts him in the most painful of times. For those who were herded into the gas chamber, the frights and insecurity must have been horrifying. Yet, when Bruno woke up that morning, he had little idea that his day and his life would end in this manner. It is for this reason that I would say that Bruno's crossing the fence is the single most important event in the book.