In Ephesus, Cerimon, a kindly doctor, and his aid Philomon provide fire and food to those suffering from the wicked storm. Two gentlemen enter, and discuss how well known Cerimon is for his charity. Then Philemon enters with a chest that has been discovered floating on the sea. Inside they find what appears to be a corpse, with a paper attached written by Pericles, asking any who find the body of Thaisa to give her a proper burial, since she was the daughter of a king.
Cerimon looks at the body and determines that she is not yet dead, and brings in some medicines. Soon she stirs, and wakes.
Meanwhile Pericles arrives in Tarsus, and tells Cleon and Dionyza about his misfortune, saying: "Should I rage and roar / as doth the sea [Thaisa] lies in, yet the end / Must be as 'tis" (III.iii.10-13). He lands at Tarsus and charges Cleon and Dionyza with the care of his child, and asks them to raise her as a noble. Cleon promises that he will, wanting to repay Pericles for the good he did Tarsus during the famine. Pericles leaves, swearing he won't cut his hair until his daughter, whom he names Marina, marries.
In Ephesus, Cerimon explains to Thaisa that some jewels and Pericles's letter lay in the chest with her. She recognizes the writing as Pericles's, and believes she will never see him again. Thus she expresses a desire to take holy order, and become one of the goddess Diana's vestal virgins. Cerimon offers to help her, and she thanks him.
Pericles here speaks but briefly of his reaction to his misfortunes, merely saying that it does no good to get upset about it, since he cannot change the things that have happened to him. Pericles statements about the world and his sincere belief that he has no agency within it cast him as an increasingly beatific "good man,' as someone almost saintly in his willingness to endure misfortune. As such a beatific man Pericles becomes almost inscrutably simple; he is reminiscent of Job, except he has no real faith, and therefore seems to have no real moral or psychological reason to believe the way he does.
Thaisa believes Pericles to be dead, and doesn't consider her child at all. She chooses basically to become a nun. The nunnery is a recurring image in Shakespeare, as the unproductive alternative to marriage. Female characters are often threatened with the nunnery if they don't obey their father in questions of marriage, as in the beginning of A Midsummer Night's Dream. The nunnery is a refuge for women in mourning; Juliet in Romeo and Juliet thought of the nunnery as an option when her world seemed to be falling to pieces. And the nunnery is also seen as a place to contain dangerous female sexuality, as when Hamlet suggests Ophelia go to a nunnery so she can stop luring men, particularly him.
Yet in all these cases the nunnery is an idea or a threat, and no one actually makes it there--except for Thaisa. Her case is somewhat different; having already been married, the nunnery for her is not a place of containment, but a place to retreat from a world she no longer cares for, if Pericles is not in it.