Combining the popular subjects of environmentalism and new technology, hybrid cars make for an ideal topic for middle-grade readers. This volume in the How Things Work series is bouncy, savvy, and, above all, clear; it is hard to come away without a working knowledge of everything from the mechanics of hybrid engines to why dependence on foreign oil is bad. Hosting the series are two cartoons – a robot and a caveman – especially apt choices for a book couched in the concept of discarding old energy sources for new. (When the caveman plugs his PHEV car into one of the robot’s sockets, the robot deadpans, “This is humiliating.”) A four-page time line explains the history of the concept, while bright cutaway illustrations show how the hybrid saves gas and how a fuel cell converts hydrogen gas. But the main event is Swanson’s gift for making complicated subjects crystalline. To explain greenhouse gases, she compares them to the heat that builds up inside a parked car because of the glass windows – a swift, germane metaphor. The back matter is a bit skimpy, but otherwise this is a model of how to make science appeal to young readers.

Booklist - Daniel Kraus **Booklist -- Starred Review ** January 9, 2015