Set in 1939 as the Nazi shadow falls over the continent, Flotsam follows displaced people, including political dissidents and Jews, who travel the unpaved roads seeking refuge. Steiner and Kern have overstayed in Czechoslovakia and are forced to leave, only to be turned away from other countries as well. Living hand to mouth and selling shoelaces and safety pins for a few pennies, they find small pleasures in Paris and in love. The novel contrasts cold-blooded laws with moments of humanity.

The novel follows the life of Theodosia Burr Alston, a brilliant, fiercely independent woman of the early American republic who is swept from a cultured New York upbringing into the jealous, ambitious world of Southern politics when she marries Joseph Alston. Torn between devotion to her charismatic but controversial father and the demands of her husband and society, she struggles with love, motherhood, loss—including the death of her young son—and the limits placed on a woman's intellect and freedom. The story traces her passionate correspondence, inner resilience, and ultimately her mysterious disappearance at sea, examining how personal loyalty and public scandal shape a life and a legend.