Half of all 7,000-plus human languages may disappear over the next century, and when they're gone, it will be forever. Ross Perlin, a linguist and codirector of the Manhattan-based non-profit Endangered Language Alliance, is racing against time to map little-known languages across the most linguistically diverse city in history: contemporary New York. Perlin recounts the unique history of immigration that shaped the city, and follows six remarkable yet ordinary speakers of endangered languages deep into their communities to learn how they are maintaining and reviving their languages.

Seke is spoken by 700 people from five ancestral villages in Nepal, a hundred of whom have lived in a single Brooklyn apartment building. N'ko is a radical new West African writing system now going global in Harlem and the Bronx. After centuries of colonization and displacement, Lenape, the city's original Indigenous language and the source of the name Manhattan ("the place where we get bows"), has just one fluent native speaker, bolstered by a small band of revivalists.

A century after the anti-immigration Johnson-Reed Act closed America's doors for decades and on the 400th anniversary of New York's colonial founding, Perlin raises the alarm about growing political threats and the onslaught of "killer languages" like English and Spanish.