On returning from the tour, Victor receives a letter from his father saying that his youngest brother, William, has been murdered. Shocked and upset, Victor and Clerval rush to Geneva. But the town gate is locked when they arrive. Victor visits the spot where his brother died. On the way he sees lightning playing over the peaks of the mountain Mont Blanc.
As family bliss and innocence are destroyed, Victor's descriptions of nature turn dark, reflecting his psyche. Lightning is a reminder of his earlier realization that mankind can never understand nature. It's a lesson he forgot, to his detriment.
Near where his brother died, Victor sees a figure resembling the monster. He realizes that the monster killed William, which means that he, Victor, is really responsible since he created the monster.
Victor realizes the cost of his arrogant assault on nature and begins to lose his innocence. And he realizes the monster is revenging itself on him.
When Victor arrives home the next day, his brother Ernest tearfully informs him that Justine has been accused of William's murder: in her pocket the police found a portrait of Victor's mother that William had been wearing.
Victor, who thought himself a creator of life, will now be responsible for the death of two innocents.
Victor announces to his family that Justine is certainly not guilty, but says no more since he fears anyone hearing his story would think him insane. But Victor is confident that Justine could not be convicted for a crime she did not commit by circumstantial evidence.
By concealing his role in William's death and Justine's fate, Victor isolates himself and must bear all the consequences of his ambition alone.