The Name of This Book Is Secret by Pseudonymous Bosch

Yes, this book has been out a while, but since it's more on the Juvenile side of fiction, I haven't picked it up before now.

Cassandra is an eleven-year-old survivalist. She's prepared for any--and every--thing. While spending time with her grandfathers who own an antique dealership, a box of items is delivered with an unusual briefcase inside. The briefcase is labeled "Symphony of Smells" and is filled with vials of different powders, each with a distinct smell. The box came from a magician's home, so Cassandra, with her new friend Max-Ernest, decides she needs to investigate. Once in the house, they find a secret room and a notebook with a riddle. They also meet the bad guys--Dr. L and Ms. Mauvais.

Cassandra knows the couple will be looking for her and Max-Ernest. She is proven correct when the two show up at her school. What she doesn't expect is Benjamin Blake--a classmate--disappears after Dr. L and Ms. Mauvais leave. Now Cassandra must convince Max-Ernest to help her save Benjamin from a fate they don't want to think about.

A good mystery and suspense novel, especially for the older elementary grades. This is written in the style of the Lemony Snicket books--so the narrator is extremely involved in the plot and the action. There is a lot of things going on with the plot, too much to explain here, but the book is pretty engrossing. And descriptive.