By day, Marguerite and Auguste feign indifference, meeting only at night to whisper, kiss, and dream of the future. Auguste suggests they could run away together in the New World, declaring that if they are together, they will have nothing to fear. They drift in a reckless idyl as the ship sails into uncharted waters.

However, the deckhands and navigator notice their meetings, and Roberval comes to suspect them. Rather than confronting Marguerite, he becomes strangely jovial, then targets Damienne, pressing her with smiling questions about whether her mistress walks the deck at night. Damienne refuses to answer, protecting Marguerite. Jean Alfonse intervenes, deflecting Roberval's interrogation, and Roberval turns suspicion on the navigator himself.

The confrontation is interrupted when the ship shudders violently. On deck, the passengers see an enormous whale—a black fish the length of their vessel—that has struck the hull. More whales appear, swarming the Lèchefraye, but by what seems divine grace, all three ships are spared. The terrified company crosses themselves.

Roberval seizes the moment to address everyone from the quarterdeck. He warns that some evils lurk beneath the waves and that wanton sinners with lustful hearts will be purged from the company, exiled, flogged, shackled, or hanged. His sermon is clearly aimed at Marguerite and Auguste.

That night at table, Roberval calls for music; Auguste plays while Roberval fixes his gaze on Marguerite alone. Unnerved, she pricks her finger with her needle and draws blood. She rises and leaves with Damienne, brushing past Auguste as she goes. Marguerite understands that Roberval has divided them and that to meet again would mean death.