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John Green Image Credit: Evan Agostini/Invision/AP

John Green fans, mark your calendar.

The author of the million-selling The Fault in Our Stars has a new novel coming October 10, Dutton Books announced Thursday. The book is called Turtles All the Way Down and tells of a 16-year girl in search of a missing billionaire as she copes with mental illness. Turtles is Green’s first book since Fault in Our Stars, which came out in 2012. According to Dutton, the new release is “about lifelong friendship, the intimacy of an unexpected reunion, Star Wars fan fiction, and tuatara. But at its heart is Aza Holmes, a young woman navigating daily existence within the ever-tightening spiral of her own thoughts.”

Green, 39, said in a statement that he had been working on Turtles for a long time.

“This is my first attempt to write directly about the kind of mental illness that has affected my life since childhood, so while the story is fictional, it is also quite personal,” said Green, who has spoken publicly about his struggles with obsessive-compulsive disorder and anxiety. He is one of the world’s most loved authors and sales just for The Fault in Our Stars, the tearjerker about two teen cancer patients, tops 45 million copies. The Fault in Our Stars was adapted into a movie of the same name starring Shailene Woodley and Ansel Elgort.

Green’s other books include Paper Towns and Looking for Alaska.