As otherworldly as the Prius Prime looks, it’s not the offspring of the Transformers leader Optimus. It’s Toyota’s plug-in hybrid variant.

The concept is simple: Charge the battery and it drives like an electric car. Once the battery is spent, the Prime drives like any other Prius. Easy peasy.

It’s not Toyota’s first plug-in. My neighbor has the first one, based on the third-generation Prius, and she has been disappointed with its real-world all-electric range of 11 miles. Prime, riding on Toyota’s new scalable chassis architecture, rectifies that. Toyota claims up to 25 miles in E.V. mode. I saw 24, restraining my inner Mario Andretti.

Math class is in session. Don’t groan: Numbers are important to plug-ins. Prime’s main competitor, the Chevrolet Volt, is rated by the Environmental Protection Agency at 53 electric-only miles. Over all, the Chevy is less efficient, at 106 miles per gallon equivalent and a 42 m.p.g. average on gasoline alone, compared with Prime’s 133 m.p.g. equivalent and 54 m.p.g. The Hyundai Ioniq plug-in hybrid, available late this fall, is estimated at 27 electric miles.