There really is no falling action to this story so this would probably be another Climax. What basically happens is Bruno goes over to Shmuel's side of the fence to explore the other side and look for Shmuel's father.
Lets go look for your Father now.
It is ok.
The conflict of Shmuel not being able to find his father left some unanswered questions. But ultimately we can infer that the two boys while in the camp searching for Shmuel's father were moved by soldiers into a gas chamber and suffered their death (later discovered by Bruno's father).
Shmuel, I am so sorry that we couldn't find your Father today.