How the Anglo-Irish Treaty between the unrecognised Irish Republic, represented by Michael Collins, and the British government was concluded after high-stakes negotiations in 1921.

British teenager Leo Colston spends a summer in the countryside, where he develops a crush on the beautiful young aristocrat Marian. Eager to impress her, Leo becomes the "go-between" for Marian, delivering secret romantic letters to Ted Burgess, a handsome neighboring farmer.