Miss Grace Callison lived in Trenton, a city in northern Missouri.

Once the site of an Utopian Socialist commune influenced by the English thinker, John Ruskin, Trenton became a center of manufacturing and food-processing.

https://en.wikipedia.org/wiki/Trenton,_Missouri

In April of 1913, Grace received a postcard from Mary McCown.

Mary mailed the postcard from Detroit, Michigan.

At this time, Detroit was a thriving center of manufacturing that attracted immigrants from many parts of Europe.

https://en.wikipedia.org/wiki/Detroit

The face of the postcard bears a photograph of “Harmonie Hall”.

This building was erected in 1893 to replace an earlier structure erected by a German-American Singing Club in the 1874.

The Singing Club was formed in 1849 when four young men (German immigrants) recruited ten others to sing German Lieder.

As in many other cities, the German Singing Club grew rapidly as German immigration grew throughout the 19th century.

https://nasaengerbund.org/about

The German Singing Club in Detroit, Gesang-Verein Harmonie, endured until the 1970’s when the building was abandoned.

The building was deemed an historic structure and was restored as a community center.

https://historicdetroit.org/buildings/the-harmonie-club

Although mailed in 1913, the postcard was printed at least seven years earlier; it was published by the Detroit News Company.

Due to the “undivided back” format, Mary wrote her name and address on the face.

Alas, there is no other information from which to infer details about the lives of Mary or Grace.

One hopes that they may have shared a deep appreciation of choral music.