Posthumus enters in chains, with his jailers. They leave him alone, whereupon he explains that he welcomes his bondage, as it is for him the way to freedom (death). He says his conscience is more of a prisoner than his body, and asks the gods to give him the "penitent instrument" (line 10) to pick this lock, setting him free forever. He feels that volunteering to be put into chains is the best way. He asks the gods to take his life for Imogen's, though "'Tis not so dear" (line 23).
He falls asleep. Solemn music sounds to signal the scene of Posthumus's dream. A group of spirits, Posthumus's ancestors and dead brothers, gather round him. They beg Jupiter, king of the gods, to intervene and help Posthumus. Jupiter descends on an eagle, and throws a thunderbolt. The spirits fall upon their knees. Jupiter is annoyed with them, but promises that he will uplift Posthumus's fortunes and that Posthumus will be reunited with Imogen.
Posthumus awakens, bitterly disappointed that his relatives have vanished. He finds a book on the ground, and hopes that the contents are worthy of the cover. He opens the book and reads a cryptic prophecy. It predicts that when a lion's whelp (Posthumus Leonatus) shall be embraced by "a piece of tender air" (Imogen), and when branches shall be lopped from a dead cedar (Cymbeline having lost his sons), but which shall later revive (restoration of the lost sons), then Posthumus shall be happy and Britain shall flourish.
Posthumus does not fully understand the prophecy, but feels it bears some likeness to his life, and so keeps it.
The jailers return and tell Posthumus that he shall be hanged. He says he is more than ready. The First Gaoler, with mordant humor, comforts him with the news that he needs fear no more tavern bills: he who dies pays all debts. The Gaoler reflects that he has never seen a person who is so eager to be hanged as Posthumus. He wishes that everyone were good, so that there would be no more gaolers or gallows. Though this would deprive him of his present job, he would hope for a better one.
Posthumus's opening lines carry an emotional power that is lacking in his earlier speeches. His request to the gods that they take him in payment for Imogen's death, coupled with his certainty that he is worth less than she, is full of pathos.
The dream scene has perhaps attracted more criticism than anything else by Shakespeare. It is written in poor quality doggerel verse, serves no dramatic purpose, and its style and language bear little relation to Shakespeare's other work, leading to doubts that it is his. The character Jupiter has been called "preposterous" and indeed, it is difficult to play this scene without arousing laughter of the wrong sort. It is possible that it was later interpolated-by Shakespeare or another writer - for a performance at the court of King James I, where elaborate masques involving gods, painted scenery and 'flying' persons supported by wires were popular. But equally, it may be that it was written by Shakespeare in one of his less inspired moments.
The scene is an example of a type of stage device which leant a new phrase to the English language: deus ex machina, Latin for, literally, the god from the machine. It originated with Greek and Roman theater, when a machine would lower a god or gods onto the stage to resolve a hopeless situation. The phrase deus ex machina has been extended to refer to any resolution to a story which does not pay regard to the story's internal logic and is so unlikely that it challenges the audience's suspension of disbelief. Its advantage is that it allows authors to end the story in the way they want.
Posthumus's hope that the book that the spirits leave behind is not merely "a garment / Nobler than that it covers" (line 134-5) recalls the theme of appearance versus reality. Symbolically, the book is important, as it marks the crossing-over of the supernatural world into the natural world. It is inevitable that Posthumus's life will be transformed as a result.
Cymbeline: Novel Summary: Act 5 Scene 4