Suppose it were possible to journey to a mirror image world from ours every four years on leap year day and return a month later by saying an appropriate word? Such is the premise of this fantasy by the prize winning Dutch author in her first English translation. Young Tom Witt has learned from his mentor Thomas Alva about such journeys and having overheard the magic word makes the transition on February 29, 1964. We learn this only gradually through his diary, for once the trip is made he loses all memory of the other world; as the diary progresses and Tom gains experience in ""World X"" along with Thomas Alva, there are more gaps than substance. We're never sure exactly why the mirror world is better (because there's no crowding? nothing is forbidden? school is an optional pleasure?). The love story between Tom and Teja is real but somehow superficial. Though the officials there are aware of, and opposed to, the travel between worlds, Tom leaves at the appropriate moment--but evidently returns in 1968, leaving this diary behind, and by 1972 has not returned; hence publication of the diary through the efforts of his brother. Unless the author plans a sequel for Tom's possible return in 1976, readers may continue to feel somehow unsatisfied by the whole experience.