Rick Riordan is well-known to young readers. “Percy Jackson and the Olympians,” “The Kane Chronicles” and “Heroes of the Olympus” were all phenomenal successes and attracted a huge readership. Riordan has created a new mythological series with “Magnus Chase and the Gods of Asgard, Book One” In this series, the author explores Norse myths. Magnus, the main character, is a troubled kid who’s told he’s the son of a Norse god. Riordan is already at work on the second book in this series, “The Hammer of Thor,” which is due on Oct. 4, 2016.