Two continents are divided by a sea, and a storm upon it called the Dragon's Breath, which stands as a great towering storm for 79 years out of every 80. In the one year it recedes, an event known as "The Opening". The sea becomes passable, triggering a Columbian Exchange-style collision: a sudden, punctuated transfer of technology, goods, disease, and people between two worlds that have spent a lifetime apart.

In one such Opening, movable type crosses into Dorynthos, a city overseen by the Temple of the Calm. The Temple of the Calm is a religious institution cast in the mould of medieval European churches. The city of Dorynthos is cast in the mould of the Hanseatic league. The resulting avalanche, based largely on the Protestant Reformation, is at first contained, then unstoppable. The diffusion of technology produces sweeping civilizational change.

The book also features a magic system rooted in linguistics and philology. Inspired by the divergence of the Indo-European languages from a single proto-tongue, it follows a league of scholars (The Letterers, a guild which preserves the records of the openings) who sift through the two living languages of Worldfall- Alkan and Mysoan- along with fragments preserved in lullabies, religious rites, children's songs, and charms, to reconstruct the binding language, lost to time.