And it was good. The tale the book builds upon is very moving: a trumpeter sounds a trumpet each hour in each of the 4 compass directions from the tower of a church in Krakow, Poland. When the city is attacked by Tartars, the trumpeter sounds the trumpet but is killed mid-hymn. In memoriam, the hymn is cut short purposefully. From this, the book is about a boy who sounds the trumpet but continues the song as a warning of danger, rather than ending it. The book was lauded for its introduction of Polish history to young readers and for the author's sensitivity to detail and culture.
Read Also:
If you'd care for a history of the time period, Harold Lamb's The March of Muscovy (and indeed, Harold Lamb in general) is a good account of Ivan the Terrible's Russia.
Margaretha Shemin's The Little Riders
And any Newbery book is recommendation on its own.