Foursome is the spirited account of the intense relationship among four artists whose strong personalities, passionate feelings and aesthetic ideals drew them together, pulled them apart and profoundly influenced 20th-century art. In 1921, Alfred Stieglitz, the most influential figure in early 20th-century photography, celebrated the success of his latest New York City exhibition, whose centerpiece was a series of nude portraits of the young Georgia O'Keeffe (soon to be his wife). It was also a turning point for both O'Keeffe and Rebecca Salsbury, the fiancée of Stieglitz's protégé at the time, Paul Strand. 

In the years that followed, O'Keeffe and Stieglitz became the preeminent couple in American modern art, spurring each other's creativity. Observing that relationship led Salsbury to encourage new artistic possibilities for Strand and to rethink her own potential as an artist. In fact, it was Salsbury, the least known of the four, who was the main thread that wove the two couples' lives together. Carolyn Burke mines this foursome's correspondence to reveal how each inspired, provoked and unsettled the others while pursuing their own artistic innovations.