“Isabella; or the Pot of Basil” is Keats's early narrative poem, completed in 1818. Its synopsis is truly sensational: Isabella, a young lady from medieval Florence, is in love with the family's servant, Lorenzo. Because of both class and economic differences between the lovers, their connection is disapproved of by Isabella's family, particularly her brothers, who decide to get rid of Lorenzo; they murder him and bury him in a forest. Isabella does not know why Lorenzo disappeared, but eventually she is visited by his ghost and finds out. In a frenzy, she runs to the forest, exhumes the body, cuts its head off and plants it in a pot with basil seeds. She spends the rest of her life crying over the pot, which she tenderly nurses. The basil plant thrives, while the girl gradually withers. When the pot is taken away from her, Isabella dies.

The story itself, which forms the basis of Keats's poem, was not the poet's invention—he took it up after Boccaccio's Decameron (day four, story five). As Miriam Allott notes, the idea was suggested by William Hazlitt's lecture “On Dryden and Pope” (February 3, 1818), which Keats attended. Keats did not depart form Boccaccio's plot, but “translating” the story from prose to verse he distinctly changed its atmosphere, emphasized some elements rather than others, incorporated his own lengthy digressions and descriptive details, and introduced “conventions of the most popular romance genre of his day, the Gothic novel.” Boccaccio's narrative is more realistic and less emotional in tone; Keats, in turn, sentimentalizes the love affair, converts Isabella's brothers into ruthless capitalists and makes the most of the grotesque potential of the narrative in order to convey his own version of the story.

According to Allott, Keats departs from Boccaccio by opening his narrative with the account of the love affair between the couple, in contrast to Boccaccio's more down-to earth beginning; moreover, he postpones the reference to Isabella's brothers till later in the narrative.