See my review of Ru Red, here. Sasha said: I'll be uploading my review to my YouTube channel abookutopia! Kerstin Gier's books, with the latest releases, covers, descriptions and availability. Reviews of and essays about children's books from The New York Timesgoodreads. Time travel, Gier style, is something to be discussed on the. Ru Red Kerstin Gier Smaragdgrün Kerstin Gier Saphirblau Kerstin Gier. Gier Kerstin Gier is the bestselling author of the Ru Red trilogy, as well as several popular novels for adults.