The Copper Beech by Maeve Binchly

In the Irish town of Schancarrig, the young people carve their initials - and those of their loves-into the copper beech tree in front of the schoolhouse. But not even Father Gunn, the parish priest, who knows most of what goes on behind Shancarrig's closed doors, or Dr. Jims, the village doctor, who knows all the rest, realizes that not everything in the placid village is what it seems.