It examines issues of conflict and war, the actions and consequences of violence, and how it can divide and oppose people who can be friends as easily as they can be enemies.

In the Republic of Ireland in the 1960s, more precisely the centre of the bridge over the river that separates the Irish villages of Carrickdowse and Ballydowse, there is a white line that few young people dare cross.

The leader of the Ballys is Fergus, the son of a pauper family and an unpromising student who lives in a trailer on the edge of Ballydowse with his mother and abusive stepfather.

After a series of battles, Fergus denounces Riley as a traitor to the cause before the final showdown which has the Ballys attacking an abandoned castle ruin defended by the Carricks.

Finally fed up, the towns' adults, including Geronimo's father and Fergus' abusive stepfather, reclaim their children.

Marie narrates the coda, expressing that she married one of the boys, and that the other became the couple's closest friend, but she does not reveal whom she chose to wed.