I.i Videna, the queen, is heartsick and complains to Ferrex. She tells Ferrex, her favorite (and elder) son, of Goboduc's plan to deprive him of his birthright by dividing the kingdom between Ferrex and his younger brother, Porrex. She accuses Porrex of "growing pride." Ferrex will not believe that Gorboduc will extend his "first injustice" towards him and will rely upon the faith his forefathers have extended to their seed. Videna fears "murders, mischief or civil sword" and "just revenge when [the] right-succeeding line returns again".

I.ii Gorboduc, describing himself as aged, addresses his wise and long-trusted counselors, Arostus, Philander, and Eubulus. He asks them their advice on his plan to divide the kingdom between his sons. Arostus agrees, saying two young men, being inexperienced, would best take the reigns from one old king, so long as he gives them the reign before he dies and can thereby guide them. Philander agrees also, but suggests a co-regency rather than divided rule—one beginning after, not during, Gorboduc's life. Eubulus argues against splitting the kingdom or the kingship, foreseeing catastrophe in any plan but direct descent. He cites Brute's legendary mistake of dividing the kingdom three ways between his sons. Only civil war could follow. Gorboduc graciously thanks them and, not fearing the nobility of his sons, chooses to divide the kingdom at the Humber. Ferrex shall take the Southern realm and Porrex the Northern.

Chorus: Iambic Pentameter rhymed ABABCC. Plays out the theme of the first dumb show of strength in unity, disaster in division.

Dumb Show: Coronet music. Enter a king and his nobles. An old man offers him wine in a glass, which he refuses. After that, a young man offers him poison in a golden cup, which the king accepts and dies from drinking. The glass is Nature, the gold flattery.

II.i In Ferrex's court, the elder son expresses his amazement at his father's decision as he speaks to Hermon (a parasite) and Dordon (a counselor that Gorboduc has assigned to him). They also express surprise. Ferrex has always been a model son and prince. Dordon suggests that Ferrex has taken his birthright early, before his father's death, which is a sign of favor, but Ferrex sees only half of his birthright. Hermon fans the flames of Ferrex's jealousy of "proud" Porrex—"so mad a man". Dordon tries to keep peace. Ferrex denies he could be a fratricide, but levies up an army to defend himself against Porrex in the event that Porrex envies his realm. Ferrex leaves with Hermon, the bad counselor, leaving Dordon, the good, alone on stage to fear the outcome of this decision.

II.ii In Porrex's court, the younger son learns of Ferrex's preparation against him and discusses the threat with Tyndar (a parasite) and Philander (a counselor that Gorboduc has assigned to him). Tyndar is quick to blame Gorboduc for having divided the realm in the first place. Philander proposes a delegation to ask Ferrex the reason for his warlike preparation. Porrex, however, jumps to the hotheaded conclusion that Ferrex means to attack and determines not to be caught unprepared. He leaves with Tyndar, the bad counselor, leaving Philander, the good, alone on stage to fear the outcome of this decision.

Chorus: Same rhyme scheme as first Chorus. Bemoans hotheaded youth and the fault of kings who do not listen to good counselors.

Dumb Show: Flute music. Enter mourners clad in black. They circle the stage thrice, representing the sorrow that rises from misgovernment and mourning the death of Ferrex.

III.i Gorboduc speaks with Eubulus and Arostus. He compares the trouble in his realm with the fall of Troy. Eubulus reads aloud a letter from Dordan stating Ferrex's intention to attack Porrex and predicting the fall of both. Arostus tries to calm Gorboduc so the king might hear good counsel and stop the war. Philander enters and tells Gorboduc of Porrex's preparation to meet Ferrex. Gorboduc cannot believe that his sons did not come to him with their complaints before heading onto the field of battle. He falls into despair. Philander, like Arostus, advises Gorboduc to intercede. A Nuntius enters with news that Porrex attacked first and killed Ferrex. Gorboduc, clearly distraught, calls for heaven to punish Porrex.

Chorus: Iambic Pentameter ABABCDCD, etc. It does little more than summarize the action.

Dumb Show: Hoboy (Oboe) music. Alecto, Megera, and Ctesiphone (the three furies) rise from under the stage. They are clad in black, spattered with blood and flames, wound with snakes. One carries a snake, another a whip, the third a firebrand. One drives before her Tantalus and Medea, another Athamas and Ino, the third Cambises and Althea—each a king and a queen who had slain their own children. They circle thrice.

IV.i Videna, the queen, enters alone. She is distracted and filled with hate against Porrex, who has killed her favorite son. She vows to kill Porrex.

IV.ii Gorboduc speaks with Arostus. He has summoned Porrex to the court. Eubulus enters with Porrex. Gorboduc upbraids Porrex for slaying his brother and gives him an opportunity to excuse himself. Porrex expresses his grief at having to do the deed, but excuses himself on the grounds that Ferrex threatened him and he merely defended himself with a preemptive strike. Gorboduc, angered, banishes Porrex. Marcella enters shortly after with news that Videna has murdered Porrex. Gorboduc asks Eubulus to kill him, but Eubulus advises him to investigate the circumstance. After Gorboduc and Eubulus exit, Marcella describes Porrex's death to Arostus.

Chorus: Iambic Pentameter ABABCC with second strophe ABABCDCDEE. Comments on the action.

Dumb Show: Drum and Flute music. Enter "hargabusiers" (horse soldiers?) and armed men, who discharge weapons as in battle and circle the stage thrice. This symbolizes civil strife.

V.i In the court of Gorboduc, Clotyn, Duke of Cornwall, Fergus, Duke of Albany, Mandud, Duke of Loegris, Gwenard, Duke of Cumberland and Eubulus all meet. The Dukes are incensed against the tyrants who have committed fratricide and infanticide. Still, they are shocked that the people have arisen and killed the "guiltless king" and the queen. Gwenard expresses the need to stay loyal to the kingship and accept the horror of bad governance as any good subject should. Even Eubulus agrees that punishment must follow the murder of Porrex by his mother, but he fears the mob, "so giddy are the common peoples minds / so glad of change." He therefore advises the Dukes to levy troops of horsemen, against which the rebellious mobs cannot compete. All exit, leaving Fergus behind, who soliloquizes that this is his opportunity to take control of the kingdom.

V.ii Eubulus enters alone. He describes the horrors and lawlessness of civil battle. The Dukes (except Fergus) enter with Arostus. They boast of putting down the rebellion. A Nuntius enters. He tells of Fergus on the march with twenty thousand men. The Dukes rush out to put down Fergus' attempted usurpation. The play ends with Eubulus' long lament that, without a lineal descendant, the country will only resound in civil strife and usurpation, which even Parliament cannot control. Only God can ultimately restore the order of the realm.