It consists of a fictionalised version of the life of Sordello da Goito, a 13th-century Lombard troubadour depicted in Canto VI of Dante Alighieri's Purgatorio.
It was harshly received at the time of its publication: Alfred, Lord Tennyson's opinion was recorded thus by William Sharp in his biography of Browning: Lord Tennyson manfully tackled it, but he is reported to have admitted in bitterness of spirit: "There were only two lines in it that I understood, and they were both lies; they were the opening and closing lines, 'Who will may hear Sordello's story told,' and 'Who would has heard Sordello's story told!'".
In a castle at Verona, the Council of Twenty-Four discuss the city's predicament; in a distant room, the poet Sordello sits motionless, thinking about his love, Palma.
Sometimes he would stare at a stone font in a vault of the castle, dreaming that the female statues who held it up were under a curse, and that he could plead with God for their pardon and release.
Impatient with Eglamor's feeble efforts, Sordello interrupts him and continues his song so effectively that, to his own astonishment, he wins the prize, and Palma bestows upon him her scarf.
Disappointed, Sordello then gives up the plan of becoming a "man of action", and devotes himself to minstrelsy, but quickly becomes bored and slapdash; he tries reinventing his language to express his visions more directly, but encounters public incomprehension and personal fatigue.
He travels to Mantua, where Sordello is appointed to welcome him with song, but the baffled troubadour, lacking inspiration, wanders back to Goito.
At Goito, Sordello re-immerses himself in his daydreams for a whole year, but he has lost his self-confidence, and he begins to wonder if he had thrown over all prospect of success as an ordinary human being, let alone as an Apollo.
His bitter musings are interrupted by Naddo, who brings news that he has been summoned to Verona to sing at Palma's wedding with Count Richard.
With contemporary Venice as a background, the rest of Book III consists of a discussion of his own hopes for the future, and his reasons for writing Sordello.)
Sordello converses with Palma, and declares himself disgusted with both the Guelphs and the Ghibellines: both sides pursue selfish ends and exploit the common people.
Even if the Utopia could be brought into being overnight by a single genius, the ideal city would crumble instantly when transferred into the hands of ordinary sinners.
Sordello's pride is touched, and, realising that this will be his last chance to express himself in any consequential way, he defends with eloquence the concept of poetry as a calling higher than any other.
When he has finished, Taurello shrugs and admits that his own life's work, seemingly more substantial, has been demolished by Ecelin's abdication, and impulsively throws the Imperial baldric on Sordello's neck, declaring him head of the house of Romano.
Should he persist in his determination to throw in his lot with the Guelphs, or does his sudden elevation to the status of a Ghibelline leader imply that his destiny lies with them?