Bruno has to leave behind his friends. Auschwitz is a concentration camp where Jewish prisoners are being tortured and killed. Shmuel is a child prisoner at the concentration camp. 

During a lonely existence at Bruno's new home, Bruno finds companionship in his Jewish friend Shmuel. As a child prisoner of the concentration camp at Auschwitz, Bruno sees Shmuel sitting on the other side of a fence. Shmuel is nine as well. He and Bruno share the same birthday. They visit one another through the fence at Auschwitz:

Bruno continues to explore the woods near his house and often finds himself at the fence spending time with Shmuel.

Truly, Bruno is inquisitive. He cannot understand why Shmuel would want to live at Auschwitz. Shmuel is starving; therefore, Bruno provides food for his new friend. The two become very close. Their friendship is a secret. Bruno finds comfort in spending time with Shmuel. In fact, when Bruno's mother learns of the horrors at Auschwitz and insists they leave Auschwitz, Bruno does not want to leave his new friend Shmuel.

When Shmuel's father becomes missing, Bruno wants to help Shmuel find his father. Shmuel provides "striped pajamas" for Bruno. Bruno puts on the "striped pajamas" and climbs under the fence to help Shmuel find his father:

Shmuel confides in Bruno that he is unable to find his father and he is worried. Bruno vows to help Shmuel look for his father; to that end, Shmuel promises to get Bruno some pajamas so that he will blend in on his side of the fence.

During their search, Bruno and Shmuel are herded into a gas chamber to their deaths. The irony is that Bruno forms a friendship to ease his loneliness. Ultimately, this friendship leads to the boys' nonexistence. 

When Bruno is killed by the Nazis, it is ironic that Bruno's father loses his own son due to the evil system he is working to support. Only a fence separated Bruno and Shmuel. Due to their great friendship, Bruno and Shmuel break down the barriers that separate them. Both boys are innocent of the evils surrounding them during war:

The Boy in the Striped Pajamas explores the beauty of a child's innocence in a time of war, the common desire we all have for friendship, and the fences—both literal and figurative—that we must all navigate and choose whether or not to break down.

Through Bruno and Shmuel's unique friendship, the reader learns of the horrors of the concentration camps that “happened a long time ago.”

The author ends with a chilling statement:

“of course...nothing like that could ever happen again...not in this day and age.”