The resolution of Boyne's work is rooted in Bruno's sacrifice for Shmuel.  In recognition of a promise he made to Shmuel and in honoring their friendship, Bruno accompanies Shmuel to the gas chamber.  In the midst of the unimaginable horror, Bruno tells Shmuel that he is "his best friend for life."  

The story's climax is reached here and the denouement is seen in the surviving members of the family.  Mother and Gretel go back to Berlin, in partial hopes that Bruno had already made his way back there.  Bruno's father struggles to determine what happened to his son.  He is able to piece together what happened and is horrified.  He recognizes his own culpability in the death of his child.  The father is relieved of his post, taken away by guards.  The father recognizes that he is responsible for the machinery that has killed his child.  There is little else that runs through his mind.  For Bruno's father, this becomes the worst of realizations.  The climax has shown each character to be tremendously impacted by Bruno's death, a reminder of the absolute pain intrinsic to the Holocaust.