As Steven helps Sadie cope with quitting her job at the Big Donut and losing Lars, Steven and the Gems must work together to deactivate an old Diamond Authority artifact called the Harmony Core before it destroys Earth.
- ISBN13 9781785868375
- Publish Date 18 January 2019
- Publish Status Out of Print
- Out of Print 15 April 2021
- Publish Country GB
- Imprint Titan Books Ltd
- Format Paperback
- Pages 128
- Language English