The Russian-American team whose 1989 collaboration, Here Comes the Cat, was ``the first Soviet/American children's book'' elaborates the story of the town mouse and the country mouse, setting it within another story about two present-day mouse brothers fascinated by letters they find in the attic of their farmhouse. The correspondence, which they enjoy reading late at night in their bunk beds by flashlight, is between their great- great-grandfather and his brother, who had moved to the city. The letters tell how each brother gets engaged and then married; other mild adventures serve to contrast their lifestyles. Meanwhile, past and present are also compared—the older mice address each other with affection but more formality, while the younger ones trade casual insults despite their underlying friendship; the meticulously designed illustrations for the present are as crisp and bright as color photos, while the letters are enlivened with marginal illustrations in a more informal style. Nicely contrived to point out that people who lead very different lives can still care about one another, and that family history can be intriguing. (Picture book. 5-8)