The Sailor Moon Junior Chapter Book #4: The Doom Tree by Tracey West

Sailor Moon and the Sailor Scouts are back! These galactic crime-fighters may look like ordinary teenage girls, but when evil arrives, they leap into action.Serena has a secret. When evil threatens, she transforms into Sailor Moon and her friends become the Sailor Scouts, defenders of the universe. And Serena's been transforming a lot recently! With the help of the Moonlight Knight, she and the Scouts have been fighting aliens from the Negaverse, who are trying to steal energy from people. But now the fight is getting personal. The aliens have attacked the Scouts and Serena's crush Darian! It's up to Sailor Moon to save them but can she do it?