Fyrst Mysjkin, romanens hovedperson og titelfigur, er en af de forunderligste skikkelser i litteraturhistorien. Omkring ham grupperer sig en lang række meget forskellige skikkelser, der alle påvirkes af mødet med denne "vise dåre". Petersburgssocieteten blir föremål för människors diskreta förakt och hån. Den handlar även om den påstått "fallna" kvinnan Nastasia Filippovna, och den omåttligt passionerade Rogozjin som älskar henne. General Yepanchin has an ambitious and vain assistant named Gavril Ardalionovich Ivolgin (nicknamed Ganya) whom Myshkin also meets during his visit to the household. Ganya, though actually in love with Aglaya, is trying to marry Anastassya Filippovna Barashkov, an extraordinarily beautiful femme fatale who was once the mistress of the aristocrat Totsky. Rogozhin is sentenced to fifteen years of hard labor in Siberia, Myshkin goes mad and returns to the sanatorium and Aglaya, against the wishes of her family, marries a wealthy, exiled Polish count who later is discovered to be neither wealthy, nor a count, nor an exile.
