The square in the city of Gaza, with the temple of Dagon on the left. It is night-time. While the rest of the Hebrews are mourning their luck, Samson maintains his faith in God’s promise of freedom. When Abimelech, the Philistine satrap, enters, he scorns the Hebrews’ God and proclaims Dagon’s superiority, which makes the Hebrews cower in fear. But Samson’s fervour incites them to defy Abimelech. He attacks Samson with his sword, but the Jew manages to grab it and kills him. The Hebrews flee and the High Priest appears and curses the Hebrews and their leader. When a messenger informs him that the Hebrews are destroying the harvest, the High Priest curses them.

As dawn breaks, the Hebrews return to offer a prayer to the Almighty, in this case in humble unison, in contrast with the rich polyphonic counterpoint of the opening chorus. Dalila appears with a number of young Philistine women, who sing about the pleasures of spring. Dalila declares that Samson has won her heart and invites him to join her in her abode in the valley of Soreck. Samson prays to protect himself from her charms and an old Hebrew warns him about the dangers it would entail. The priestesses dance a voluptuous dance and then Dalila sings about spring again, after which the old Hebrew repeats his warning. Samson struggles with his desire to look Dalila in the eyes, aware that giving up to it would bring about his ruin.

In the second act, Dalila is sitting on a rock outside the entrance to her retreat in the valley of Soreck. She is delighted with the power she has over Samson and is convinced that he will end up succumbing to her charms. The thunder and lightning of an ever closer storm can be heard and seen. The High Priest arrives and informs Dalila that the Hebrews have defeated the Philistines. He offers her gold for capturing Samson, but she refuses, as she acts driven only by hatred and loyalty to her gods. They sing an energetic duet of hatred and she promises to discover the secret of Samson’s strength.

When she is alone, Dalila wonders whether she will achieve her aim. Soon after, Samson appears to bid his last farewell to her, aware that duty calls him to lead the Hebrews to victory. Unavoidable as it seemed to be, and after Dalila’s requests, Samson ends up admitting that he also loves her. After singing the most famous aria of the work, in which she asks him to revive his old love, Dalila pretends to question Samson’s love and asks him to reveal the secret of his strength, but he refuses to do so. The noise of the rolling thunder is interpreted by Samson as an expression of God’s anger. She scorns him and runs into her dwelling. Samson is momentarily torn but soon follows her. Then, several Philistine soldiers come out of hiding and Samson immediately realizes that he has been betrayed.

In a prison in Gaza, Samson, blind and shackled, with his hair cut, turns a mill wheel. Grief-stricken and overcome with remorse, Samson offers his life in sacrifice while the Hebrews, lamenting the downfall of their leader, can be heard in the distance. Inside the temple of Dagon, the Philistines are preparing a sacrifice to celebrate their victory and the scene turns into a wild bacchanal. Then, Samson enters, led by a child, and the High Priest as well as the crowd scorn him. Dalila admits that she had pretended to love him out of hatred and a desire for revenge. Therefore, there is no doubt about her treason now. The Philistines continue with their celebrations in honour of Dagon and the High Priest asks the child to lead Samson to the centre of the temple so that everyone can see him and mock him. Samson whispers to the child to take him to the two marble columns which hold the building. When the celebrations reach their climax, Samson invokes God to let him carry out his revenge and, with a supreme effort, he is able to knock down the columns, which makes the whole temple collapse, crushing all the Philistines as well as he himself under the rubble. Immediately after that, the curtain falls.