"Jepp, Who Defied the Stars," by Katherine Marsh Self-conscious about your body? Unsure where - or if - you'll ever fit in? Wondering when people will start treating you like an adult? Katherine Marsh's "Jepp, Who ­Defied the Stars" delves into these perennial adolescent challenges while transporting her readers to a tiny island in Denmark in the late 16th century - and without the help of either time machine or wizard. Instead Marsh turns to one of history's ­real-life magicians, the brilliant, eccentric astronomer Tycho Brahe, to welcome her readers to his castle-cum-­observatory, Uraniborg. A Danish noble, Brahe lacks the renown of his apprentice, Johannes Kepler, but he made similarly significant contributions to astronomy, especially for a pioneer whose work was unaided by the yet-to-be-invented telescope. Kepler's discoveries about planetary motion rest on the work of the half-scientist, half-Mad Hatter Brahe, who kept a dipsomaniac moose as a pet, and a dwarf named Jepp as court jester. In the novel, the fictionalized Jepp travels from his home in Astraveld, a kind of crossroads "claimed by both the Spanish Netherlands and the Protestant North," to the Infanta Isabella's palace in Brussels, and then from Brussels on to the "intricate universe" of Uraniborg. There Jepp will be delivered from the status of a dog at Brahe's feet, dependent on scraps from his master's dinner, to that of an esteemed scientist in his own right. Narrating a young adult novel from a dwarf's perspective is nothing short of inspired. Jepp's physical form may be a ticket out of poverty to the castles of royalty and aristocrats, but it also amplifies the miseries of adolescence. Readers will feel an immediate sympathy for the eternally child-size Jepp, allowed the luxuries of court life for the price of his dignity. As demonstrated by the recent dystopian swell, the themes of Y.A. fiction - bullying, sexual confusion, substance abuse, delinquency, identity, first love and broken hearts - have never been lighthearted. But Marsh pushes these aside to focus on the central and unanswerable question of free will. Does it exist? Or, to couch the question in an era in which astrology was a "sister art" to astronomy, Can man defy the stars and direct his own destiny? Predestination is a heavy topic, but in this case it is leavened by Marsh's meticulous research into the strange lot of court dwarves, and the wonderful and outlandish world of one of history's more idiosyncratic geniuses, whose behavior provides virtually unlimited amusement. Having lost his nose in a duel, Brahe (in fact as well as fiction) wears a prosthetic one, copper for ­everyday and silver on formal occasions. From his lowly vantage, it falls to Jepp to retrieve the nose when it inevitably slips off the astrologer's face, whether from exertion or intoxication. As Jepp comes of age he also comes to believe what all good novelists know: Fate is character, and character cannot be forged by the placement of stars in the firmament. The questions that torment Marsh's diminutive hero are not much different from those we try to answer in the present day. Are we our DNA or the sum of our experiences? Is each person's identity the result of a mysterious interplay between what nature gives him and nurture either awakens or smothers? "It is our misfortunes and our mistakes that are our true parents," Jepp decides. Like all humans, he can be passively buffeted by circumstance or he can apply his will to working with what life has given him. Jepp does, as the title of Marsh's novel announces, defy what another less gifted and determined young man might accept as fate, just as Marsh transcends genre to create an engaging narrative complex enough to keep not-so-young adults turning its pages. After a series of misadventures, he even gets the full-size girl of his dreams, one whose kindness reveals Jepp to himself as "a centaur by moonlight," a powerful and virile figure, formed differently from others, perhaps, but possessing chivalry, intelligence and grace nonetheless. Kathryn Harrison is writing a biography of Joan of Arc. Her most recent book is "Enchantments," a novel.