At the beginning of Act III the comedy turns to tragedy. Even the weather has become hot and "the mad blood stirring" (III,i,4). First, Mercutio is slain by Tybalt, and, then Tybalt by Romeo. Ironically, Mercutio, who seemed to be a pivotal player in the comedy, becomes not only the first to die, but his death makes all those that follow inevitable. "Inevitability" is the force which governs the world of tragedy. From the time of Mercutio's death the characters seem to have no control over the events as they speed by. A sense of doom is dominant; events occur before they can be stopped; perceptions are marred; errors in judgment are rampant; everyone is inflexible; everything is absolute, inevitable. The stage has been set for the tragedy.
In his 1562 narrative poem The Tragical History of Romeus and Juliet , Arthur Brooke translated Boaistuau faithfully but adjusted it to reflect parts of Chaucer's Troilus and Criseyde .  There was a trend among writers and playwrights to publish works based on Italian novelles —Italian tales were very popular among theatre-goers—and Shakespeare may well have been familiar with William Painter 's 1567 collection of Italian tales titled Palace of Pleasure .  This collection included a version in prose of the Romeo and Juliet story named "The goodly History of the true and constant love of Romeo and Juliett" . Shakespeare took advantage of this popularity: The Merchant of Venice , Much Ado About Nothing , All's Well That Ends Well , Measure for Measure , and Romeo and Juliet are all from Italian novelle . Romeo and Juliet is a dramatisation of Brooke's translation, and Shakespeare follows the poem closely but adds extra detail to both major and minor characters (in particular the Nurse and Mercutio).