The use of video games will give this instant appeal to middle grade readers, and it was well done to have the game be involved in the mystery. The real life parallels of finding clues in the apartment, and later, using escape room game skills to help Isabel get out of her house were fascinating even if the reader does not play games.
Isabel, a transplant from New York City, has a different view of the San Fernando Valley than Caleb and Ted do, and seeing it through her eyes (and seeing her through Ted's) creates some interesting juxtaposition. I love it when a city or area is so richly described throughout a book so that it almost becomes a character. Isabel's recent loss of her mother gives her father a good excuse for moving cross country, and isn't talked about excessively.
Caleb's family situation is realistic as well, and not overdone. The best family situation is, of course, Ted's. His father brings his own quirkiness to the family-- he is of Jewish descent, with family back in New York, teaches English literature, and has an obsession with a catalog of French farmhouse furniture. Ted's mother is of Japanese descent and was raised in Hawaii, but came to California to study as a nurse. Using this cultural background to then bring in WWII history was especially brilliant.
This book will appeal to a wide audience. Readers who enjoyed Schreiber's Game Over, Pete Watson will enjoy the video game component; fans of Fitzgerald's Under the Egg will enjoy reading more about the Monuments Men; detective story aficionados will revel in the inclusion of The Maltese Falcon story. This is a great book to hand to just about any middle grade reader since the cover is bright and appealing and the story highlights good friends involved in an intriguing mystery.