The play begins when the ghost of Andrea and the spirit of Revenge enter the scene. Andrea informs the audience that during his life, he was a nobleman at the Spanish court. The ghost then tells the story of his last days, how in the prime of his youth he won the love of the beautiful Bel-Imperia, but was soon thereafter killed in battle between Spain and Portugal.
Andrea's narrative then shifts to what happened after his death. He "descended straight" down to a classically pagan underworld or Hell, where he arrived at the river of Acheron only to be blocked passage by the ferryman Charon, because of his unperformed funeral rites. When his friend Horatio finally performed his rites three days later, Andrea descended into the underworld where he came to sit before three judges, Minos, Eacus and Rhadamant, who were to determine which "field", or area of the underworld, he should spend the rest of eternity—the field of the lovers or of the warriors. The judges are conflicted over their placement of Andrea because of the circumstances surrounding his death: Andrea died in war, but seems to have died for the love of Bel-Imperia. So, Minos decides to defer the matter to Pluto, king of the underworld. On his way to the palace of the king, Andrea came to a place with "three ways," the right one leading to the field of the lovers and the warriors, the left one to "deepest hell" of villains in eternal torment, and the middle way to the Palace. Taking this middle way, he soon arrived at the palace, where Proserpine, Pluto's wife, took a special interest in his case and asked if she could be his judge. After which, according to Andrea, she immediately sent him, along with the spirit of Revenge, through the gates of horn into the world, which, according to Andrea, is the last thing he remembers before arriving "here," at the start of the play.
The spirit of Revenge then goes on to predict that Andrea will see his killer, Prince Balthazar of Portugal, slain by Bel-Imperia and explains that he and Andrea will now both watch and serve as the chorus for the tragedy that they and the audience are all about to witness.
The first scene begins the play's exposition, where we are introduced to the play's key characters and themes. The plot of The Spanish Tragedy is a tragic one, full of love that is cut short, violence, the delay of justice, and the clamoring of voices for revenge.
The first scene grounds the plot in three important ways. First, we are given the narrative background of the main story: Andrea and Bel-Imperia's ill-fated love, Andrea's death at the hands of Balthazar, and Andrea's desire for revenge. Using a very ornate rhetorical style—with a great deal of alliteration, assonance, and consonance—Kyd sets up the narrative that will follow. It should be noted, though, that it is not Andrea's death but his friend Horatio's death that will provide the impetus for the play's bloody end. In fact, it should be noted that Andrea's case for revenge is rather weak; he was killed in a fair, if uneven battle, and an Elizabethan audience would have little sympathy for his desire to even the score. In fact, the main revenge plot of the play takes a long time to get started, and it is not until Act II, scene v that we will see the principal murder to be avenged and the emergence of Hieronimo as the play's tragic protagonist and avenger.
Second, the scene sets the mood and tone of the story and creates its "moral universe." Andrea's speech is delivered in measured blank verse, occasionally lapsing into rhyme, and his tone is serious and vengeful. And he inhabits a mixed Christian/pagan universe, which draws on Virgil's Aeneid for its geography of the underworld, though in a slightly expanded version with the introduction of a "third way" for souls like Andreas who do not fit neatly into either the group of lovers or the evil who are punished horribly for their crimes. Such a "third way" is necessary if we are to have a figure like Andreas, a figure who still has some interest in the world and who has not moved on to the next life completely. This world is one in which justice is delayed, where the judges of the underworld pedantically argue and are unable to come to conclusions, and where the final judges (Pluto and Proserpine) send Andreas on a quest for revenge, a tactic that will introduce further delay in the pursuit of justice as the machinations of revenge work their way to fruition. Such delays, with eventual vindication, have been seen as demonstrations of the Medieval commonplace "Truth is the daughter of time", a favorite subject of sermons; in other words, one of the play's main themes is the delay of justice and its eventual realization through that delay.
In a properly Christian world, revenge would be strictly in the hands of God, but in the play, Proserpine endorses revenge, and it is she who sends Andreas through the gates of horn (the gates through which true dreams come) so that he can revenge himself on his killer. The arrival through the gates of horn indicates that we should believe Andreas and Revenge in what they say. And the endorsement of revenge places the play in a universe somewhat, though not completely, removed from the world of the ordinary Elizabethan, for whom revenge was a controversial issue.
Finally, the play introduces us to its theatrical world, where we are quickly introduced to several important structural features, or conventions, that the play uses. Many of these are drawn from Senecan tragedy. Seneca was a Roman playwright of the first century A.D., whose bloody, sensationalistic plays were widely read by Elizabethans and used as models for Elizabethan tragedy, especially revenge tragedy. Revenge tragedy was a sub-type of tragedy where the primary motivation for the protagonist is revenge. The Spanish Tragedy is perhaps the earliest extant version of such a tragedy, and Shakespeare's Hamlet is undoubtedly the most famous.
Conventions of Senecan tragedy that we have already seen include: the angry ghost, calling from revenge from beyond the grave; the brief expository speech made by that ghost in order to inform the audience of the play's back-story; and the chorus composed of Andreas and Revenge. But as with Virgil, Kyd does not blindly copy the theatrical conventions of Seneca. The chorus is unlike anything in Seneca; it does not merely comment but, rather, has a perceived and direct interest in the action, and Andreas is introduced to us as a full-blooded character in his own right. In effect, Kyd places two mediating characters between us and the central action of the play, and these two act as an audience to the events of the play, while we perceive them as being part of the play itself. This ambiguous actor/audience status also serves to make ambiguous the relationship between the world of life and the world of the play, as we are more ready to identify real life with the events of the main plot that Andrea and Revenge watch as if they were at a play. Thus, this meta-theater setup conveys an ambiguity not only about the distinction between the "play" and "reality" but also makes ambiguous the line between the natural world and the supernatural.