Prince Lev Nikolayevich Myshkin, a fair-haired young man in his late twenties and a descendant of one of the oldest Russian lines of nobility, arrives in St. Petersburg on a November morning. He has spent the last four years in a Swiss clinic for treatment of his "idiocy" and epilepsy.
Myshkin's only relation in St. Petersburg is the very distant Lizaveta Prokofyevna Yepanchin. Madame Yepanchin is the wife of General Yepanchin, a wealthy and respected man in his late fifties. The prince makes the acquaintance of the Yepanchins, who have three daughters, Alexandra, Adelaida, and Aglaya, the latter being the youngest and the most beautiful.
General Yepanchin has an ambitious and rather vain assistant by the name of Gavril Ardalyonovich Ivolgin (nicknamed Ganya) whom Myshkin also meets during his visit to the household. Ganya, though he is actually in love with Aglaya, is in the midst of trying to marry Anastassya Filippovna Barashkov, an extraordinarily beautiful "fatal woman" who was once the mistress of the aristocrat Totsky. Totsky has promised Ganya 75,000 rubles if he marries the "fallen" Nastassya Filippovna. As Myshkin is so innocent and naïve, Ganya openly discusses the subject of the proposed marriage in front of the prince.