Liar and Spy by Rebecca Stead

This book was on a recommended list for 2012, and I gave it a rating of four out of five. Georges (the S is silent) moves into an apartment building after his dad loses his job. He discovers a note about a spy club posted in the basement, and he meets a boy named Safer. Safer and his sister, Candy, do not go to school, and Safer asks Georges to help him spy on a resident named Mr. X. Mr. X always dresses in black, and Safer has seen him doing some suspicious things. They're not sure what the man is up to, but murder is not out of the question. Georges isn't sure how far he'll go to help Safer, but he's the only friend he has right now. When Safer asks Georges to help him break into the man's apartment, Georges wonders if that's too dangerous and illegal.

The plot was interesting, and Safer is an eccentric character. He never leaves the building, and he's discovered different ways to spy on other residents. The plot offers a twist later in the book when Georges discovers a startling secret about Safer. Their relationship takes a dramatic turn but helps to solve the mystery.