Who is Levi Katznelson from The Things a Brother Knows and what is their importance?

Levi Katznelson is a seventeen-year-old high school boy who lives with his parents and his older brother, Boaz, in a small community outside Boston, Massachusetts. Levi loves and admires his older brother and had always wanted to be just like him. Boaz has been gone three years while serving with the Marines on a foreign battlefield.

When Boaz comes home, Levi knows immediately that something is very wrong with him. He confides in his best friends, Pearl and Zim, but they think Levi is overreacting. He tries to talk to his parents and grandfather but they all agree that Boaz will be fine. He'll be his old self again. He just needs time to readjust to civilian life.

Levi does some investigating and learns that his brother has plans - plans that are much different than what he told his family. Boaz is uncommunicative and remote. He barely talks and rarely comes out of his locked bedroom. When Levi is able to get inside his room, he sees that he has maps all over his room and is planning something big and mysterious. Levi hacks into Boaz' email and learns that Boaz is meeting up with some fellow soldiers and a network of soldier families but he doesn't know why.

After Boaz leaves, Levi is able to track him down in a very different locale than what he had told his family. Levi sticks with his brother and eventually learns what his brother's "mission" is, why he's been so secretive, some of the horrid experiences he had, and that his brother loves him as much or more than he ever had.