The play is set in the quiet community of Baile Beag (later anglicised to Ballybeg), in County Donegal, in 1833. Many of the inhabitants have little experience of the world outside the village. In spite of this, tales about Greek goddesses are as commonplace as those about the potato crops, and, in addition to Irish, Latin and Greek are spoken in the local hedge school. Friel uses language as a tool to highlight the problems of communication — lingual, cultural, and generational. Both Irish and English characters in the play "speak" their respective languages, but in actuality it is English that is mostly spoken by the actors. This allows the audience to understand all the languages, as if a translator was provided. However, onstage, the characters cannot comprehend each other. This is due to lack of compromise from both parties, the English and Irish, to learn the others' language, a metaphor for the wider barrier that is between the two parties.
The action begins with Owen (mistakenly pronounced as Roland by his English friend), younger son of the alcoholic schoolmaster Hugh and brother to lame aspiring teacher Manus, returning home after six years away in Dublin. With him are Captain Lancey, a middle-aged, pragmatic cartographer, and Lieutenant Yolland, a young, idealistic and romantic orthographer, both working on the six-inch-to-the-mile map survey of Ireland for the Ordnance Survey. Owen acts as a translator and go-between for the English and Irish.
Yolland and Owen work to translate local placenames into English for purposes of the map: Druim Dubh, which means "black shoulder" in Irish, becomes Dromduff in English, and Poll na gCaorach, meaning "hole of the sheep" in Irish, becomes Poolkerry. While Owen has no qualms about anglicising the names of places that form part of his heritage, Yolland, who has fallen in love with Ireland, is unhappy with what he perceives as a destruction of Irish culture and language.
A love triangle between Yolland, Manus, and a local woman, Máire, complicates matters. Yolland and Máire manage to show their feelings for each other despite the fact that Yolland speaks only English and Máire only Irish. Manus, however, had been hoping to marry Máire, and is infuriated by their blossoming relationship. When he finds out about a kiss between the two he sets out to attack Yolland, but in the end cannot bring himself to do it.
Unfortunately, Yolland goes missing overnight (it is hinted that he has been attacked, or worse, by the elusive armed resistance in the form of the Donnelly twins), and Manus flees because his heart has been broken but it is made obvious that the English soldiers will see his disappearance as guilt. It is suggested that Manus will be killed as he is lame and the English will catch up with him. Máire is in denial about Yolland's disappearance and remains convinced that he will return unharmed. The English soldiers, forming a search party, rampage across Baile Beag, and Captain Lancey threatens first to shoot all livestock if Yolland is not found within twenty-four hours, then evict the villagers and destroy their homes if he is not found within forty-eight hours. Owen then realizes what he should do and leaves, seemingly to join the resistance. The play ends ambiguously, with the schoolmaster Hugh drunkenly reciting the opening of Virgil's Aeneid, which tells of the inevitability of conquest but also of its impermanence. Yet, Hugh's stumbling attempts at recitation are evidence that our memory is also perennially mutable.
Friel's play tells of the struggle between England and Ireland during this turbulent time. The play focusses mainly on (mis)communication and language to tell of the desperate situation between these two countries with an unsure and questionable outcome.