In the Dublin of 1922 with Civil War about to break out, working class Annie Reilly is thrilled to win a scholarship to Eccles Street Convent School.

A little frozen out by her old friends, yet not wholly accepted by all of her new classmates, she is pleased to be befriended by Susie O'Neill an easy-going girl from a much more comfortable background.

Through Susie's brother, Annie meets Peter Scanlon, a neighbour of the O'Neill's and a pupil at Belvedere college. Having been radicalised by the execution of Kevin Barry, another Belvedere pupil, Peter becomes involved with the rebels who oppose the Treaty with Britain, and who are in conflict with the forces of the newly formed Irish Free State.

As families and friends across the nation are forced to choose sides, and with Peter's conservative parents unaware of the dangerous role their son is adopting, Annie and Peter find their friendship coming under strain.