Dircea begs her father Matius not to rebel against the law, which requires the annual sacrifice of the young virgin of the noble family to Apollo. The name of the victim determines the lot. Only the royal daughters are spared from the terrible duty, and even then because they were sent by the father outside the country. But Matusius believes that he, a subject, in his fatherhood is equal to the king, and in justice the king must either return his daughters to his homeland and thus show an example of strict observance of the sacred laws, or release all of them from their execution. Dircea believes that the rulers – above the laws, Matusius does not agree with her, he does not want to tremble with fear for his daughter – or let Demophon tremble just like the others!
Demofont calls his son Timant to the palace. He leaves the military camp and hurries to the call. Timant is in a secret marriage with Dirce. If their secret opens, Dirce will die for daring to marry with the heir to the throne. Timant is happy to meet with Dirce and ask her about their son Olinta. Dirceya says that the boy, like two drops of water, is like his father. Meanwhile, the term of the annual sacrifice is approaching. It will soon be known who of the young maidens is doomed to slaughter. The king often asked the oracle when Apollo will have mercy and will cease demanding human sacrifices, but the answer was brief and dark: “The wrath of the gods will subside when an innocent usurper learns of himself the truth.” Dirceya is afraid of the coming lot. She is not afraid of death, but Apollo demands the blood of an innocent virgin, and if Dirceia silently goes to the slaughter, then he will provoke God, and if he reveals the secret, he will provoke the king to anger. Timant and Dirceya decide to confess all over to Demofont: for the king issued a law, the king can and abolish it.
Demofont declares to Timant that he intends to marry him to the Phrygian princess Creusus. He sent his youngest son, Kerinth, after her, and the ship must arrive soon. For a long time Demophon could not find a worthy Timant bride. For this he forgot the long feud of Thracian and Phrygian kings. Timant expresses bewilderment: why his wife must necessarily be royal blood? Demophon insists on the need to honor the behests of ancestors. He sends Timant to meet his bride. Left alone, Timant asks the great gods to protect Dirce and protect their marriage.
The Phrygian princess arrives in Thrace. Kerint had made love to Creus during the journey. Left alone with Kreusa, Timant persuades her to refuse marriage with him. Creus is offended. She asks Carinth to avenge her and kill Timant. As a reward, she promises him her heart, arm and crown. Seeing that Kerinth pale, Creusa calls him a coward, she despises a lover who speaks of love, but is not able to stand up for the honor of a loved one with a weapon in his hands. In the wrath of Creus, Kerinth seems even more beautiful.
Matusius decides to take Dircei out of Thrace. Dircea suggests that the father found out about her marriage to Timant. She can not leave her husband and son. Timant declares to Matusia that he will not let Dirce, and it turns out that Matusius does not know about their marriage and therefore can not understand why Timant interferes in their affairs. Matusius tells us that Demofont was angry with him for the fact that he, a subject, dared to compare himself with the king, and, in punishment for obstinacy, ordered to sacrifice Dirce, without waiting for the lot. Timant persuades Matusia not to worry: the king is quick-witted, after the first outburst of anger he will surely cool down and cancel his order. The chief of the guard Adrastus grabs Dirce. Timant prays the gods to give him courage and promises Matusius to save Dirce.
Creusa asks Demophon to let her go home to Phrygia. Demofont thinks that Timant frightened Creus of his rudeness and impoliteness, because he grew up among the warriors and not accustomed to tenderness. But Creusa says that she should not listen to refusal. Demophon, believing that the guilt of the princess is all the fault, promises her that Timant will become her husband today. Creusa decides: let Timant obey the will of his father and offer her his hand, and she will make her self-esteem and refuse him. Creusa reminds Demofont: he is a father and a couple, which means that he knows what the will of the father and the punishment of the king is.
Timant begs Demophon to spare the daughter of the unfortunate Matusius, but Demofont does not want to listen: he is busy preparing for the wedding. Timant says that he has an irresistible dislike for Creus. He again begs his father to spare Dirce and confesses that he loves her. Demofonte promises to keep Dirce’s life if Timant obeys his will and marries Creus. Timant replies that he can not do it. Demofont says: “Prince, until now I spoke with you as a father, do not force me to remind you that I am a king.” Timant equally respects the will of the father and the will of the king, but can not fulfill it. He understands that he is to blame and deserves punishment.
Demofont complains that everyone insults him: a proud princess, a disobedient subject, a daring son. Realizing that Timant would not obey him, while Dircea was alive, he gave the order to immediately take Dircei to the slaughter. The common good is more important than the life of an individual: the gardener cuts a useless branch so that the tree grows better. If he had kept it, the tree might have died.
Timant tells Matusius that Demofont remained deaf to his pleas. Now the only hope of salvation is flight. Matusius must equip the ship, and Timant will in the meantime deceive the guards and kidnap Dirce. Matusius admires the nobility of Timant and marvels at his dissimilarity with his father.
Timant is firm in his determination to flee: his wife and son are more precious to him than the crown and wealth. But here he sees Dirce in a white dress and a flower crown leading to the slaughter. The dirce convinces Timant not to try to save her: he will not help her anyway and will only ruin herself. Timant is furious. Now he will never stop at anything before anyone, he is ready to... put a palace and a temple, priests, fire and sword.
The dirce prays the gods to save Timante’s life. She turns to Creus for intercession. Dirceya tells that she was innocently sentenced to death, but she does not ask for herself, but for Timantha, who is threatened with death because of her. Creus is astonished: at the threshold of death, Dircei does not think of himself, but of Timant. Dirceya asks nothing about not asking her: whenever she could tell Creus all her misfortunes, the heart of the princess would be ripped from pity. Creus admires the beauty of Dirce. If the daughter of Matusia could even touch her, then there is nothing strange about the fact that Timant loves her. Creusus can hardly hold back his tears. It hurts her to think that she is the cause of the sufferings of lovers. She asks Kerint to subdue the giants of Timant and to keep him from reckless actions, and she herself goes to Demofont to ask for Dirce. Kerint admires the generosity of Kreusa and again tells her about his love. A hope for reciprocity awakens in his heart. It is very difficult for Creus to pretend to be harsh, she is sweet to Kerinth, but she knows that she must become the wife of the heir to the throne. She regrets that vain pride makes her a slave and makes her feelings suppress.
Timant and his friends capture the temple of Apollo, overturn the altars, extinguish the sacrificial fire. Appears Demofont, Timant does not admit him to Dirce. Demophon orders the guard not to touch Timant, he wants to see what the filthy insolence can reach. Demofont throws down his weapon. Timant can kill him and offer his unworthy lover a hand, still steaming from the blood of his father. Timant falls to Demofont’s feet and gives him his sword. His crime is great, and he has no forgiveness. Demofont feels his heart tremble, but takes control of himself and orders the guards to tie Timant in a chain. Timant submissively substitutes his hands. Demofont tells me to kill Dirceu right now, in his presence. Timant can not save his beloved, but asks his father to have mercy on her. He discovers to Demofont that Dircei can not be sacrificed to Apollo, for God requires the blood of an innocent virgin, and Dircea’s wife and mother. The sacrifice is postponed: we must find another victim. Dirceya and Timant are trying to save each other, everyone is ready to take all the blame on himself. Demophon orders to separate the spouses, but they ask permission to be together at the last hour. Demophon promises that they will die together. The couple are saying goodbye.
The chief of the guard, Adrastus, gives Timant the last request of Dirce: she wants Timant to marry Creus after her death. Timant with anger refuses: he will not live without Dirce. Kerint appears. He brings the glad tidings: Demofont relented, he returns to Timant his father’s love, wife, son, freedom, life, and all this happened thanks to the intercession of Kreusa! Kerint tells how he led to Demofonte Dirce and Olint and the king with tears in his eyes hugged the boy. Timant advises Kerint to offer a hand to Creuse, then Demofonte will not have to blush for violating the word given to the Phrygian king. Kerint answers that he loves Creus, but does not expect to become her husband, for she will give her hand only to the heir to the throne. Timant renounces his rights as an heir. He owes life to Kerinth and, giving him the throne,
At this time, Matusius learns that Dirceya is not his daughter, but Timant’s sister. The wife of Matusius before her death handed her husband a letter and made him swear that he would read it only if Dircee was in danger. When Matusius was preparing to flee, he remembered the letter and read it. It was written by the hand of the late queen, who certified that Dirceya was a royal daughter. The queen wrote that one more letter was hidden in the palace temple, in the place where no one except the king can access it: it explains the reason why Dirceya was in the house of Matusius. Matusius expects that Timant will be delighted, and does not understand why he is turning pale and trembling… Left alone, Timant gives himself up to despair: it turns out that he married his own sister. Now it is clear to him that he was attracted to the wrath of the gods. He regrets that Creusa saved him from death.
Demofont comes to embrace Timant. He withdraws, ashamed to look up at his father. Timantne wants to see Olinta, drives Dirce. He wants to retire into the desert and asks everyone to forget about him. Demophon is in alarm, he is afraid that the son is not damaged in his mind.
Kerint convinces Timant that he is not guilty of anything, because his crime is involuntary. Timant says he wants to die. Appears Matusius and declares to Timant that he is his father. Dircea says that she is not his sister. Timant thinks that, in order to comfort, they deceive him. Demofont says that when the queen had a daughter, and the wife Matusia – the son, the mothers exchanged children, so that the throne had an heir. When Kerinth was born, the queen realized that she had deprived her son’s throne. Seeing how Demofont loves Timant, she did not dare to reveal a secret to him, but before she died she wrote two letters, she gave one to her confidante, the wife of Matusius, and hid the other in the temple. Demofont tells Creuse that he promised her as his son’s son and heir to the throne and is now happy that he can keep his word without resorting to cruelty: Kerinth is his son and heir to the throne. Kreusa accepts Kerinth’s proposal. Kerinth asks the princess if she loves him. Creusa asks her consent to be considered an answer. Here, only Timant understands that he is the innocent usurper that the oracle talked about. Finally Thracians are spared from the annual sacrifice. Timant falls to the king at his feet. Demofont says that he still loves him. Until now, they loved each other on duty, from now on they will love each other by choice, and this love is even stronger.
The chorus sings that joy is stronger when it comes to the heart, dejected by misfortune. But is the world perfect, where it is necessary to go through suffering in order to enjoy it in full?