Park's (""A Single Shard"") novel, set in 1999, is part history lesson, part martial arts adventure; it begins with a rather shaky premise but quickly pulls in readers. Twelve-year-old Kevin, a Korean-American math whiz who dislikes social studies (""Names and dates and places from ages ago. Boring, boringer, boringest""), is shocked to discover an arrow -and the archer who took its aim -in his bedroom one afternoon. The intruder identifies himself as ""Koh Chu-mong, Skillful Archer,"" and Kevin nicknames him ""Archie."" A search on the Internet reveals that Archie was born in 55 B.C. and founded the Koguryo kingdom (now Korea); he explains his chronological detour to Kevin: ""I lost my balance, fell off the tiger, and landed here."" Kevin raises the same questions that readers may have (""Fell off a ""tiger""? Who ""was"" this guy?""). But the logistics soon take a back seat to Kevin's breakneck mission to discover enough details about Archie to return the king to his own place and time. Along the way, popular folktales about this Korean hero come to light, and a credible friendship grows between man and boy. The conclusion wraps hastily, and supporting characters, including a museum curator and Kevin's parents come off sketchily. But the relationship between Kevin and Archie, and their race against the clock (with the Chinese Zodiac and Kevin's math skills both playing a part) to set things right will keep the pages turning. Ages 9-13. ""(May)"" .