A plague has begun in Florence, and Cosimo sends a carriage to escort Galileo, Virginia, Mrs. Sarti, and Andrea to safety. Galileo makes sure that Virginia and Andrea get into the carriage, but ultimately decides that he can’t go himself, as he has too much work to do. Sarti decides that she must stay with him, as well.
As with the age of Cosimo, the plague in Florence is a historical reality that Brecht turns to symbolic use. Little of consequence happens in scene five, except that a precedent is set for the speed at which a contagion can infect a population.
Later, Galileo can’t find Mrs. Sarti and he goes out into the street looking for her. No one will talk to him, and they run away when he approaches. He discovers that Mrs. Sarti has abandoned the house and collapsed up the road with the plague. Soldiers come and barricade the street, and Galileo becomes terrified that he’ll starve to death. An old woman agrees to help him. Shortly thereafter, Andrea appears. He’s run away from the carriage, but the authorities won’t let him see his mother, as she’s too sick. He has, however, managed to sneak past the soldiers to get to Galileo.
The soldiers act to stop the spread of the plague in much the same way that the Church will act to stop the spread of Galileo’s ideas. Here, Brecht foreshadows how ineffective that attempt will be. While the soldier’s authority (and ability to kill) frightens some people like Galileo and the old woman, others, like Andrea, manage to navigate around the soldiers with complete impunity.
Andrea begins to cry, and Galileo comforts him with news of all he’s discovered in the boy’s absence. As they’re discussing this, the soldiers return with bread for the quarantined citizens. Galileo asks them if they can bring him a book he needs. They laugh at this, but Andrea agrees to fetch it.
Much like his earlier conversation with Sagredo, Galileo asking for a book in the midst of a deadly plague makes him seem a bit insane. It shows him as a great man but also hints at the costs of that greatness.