In Britain, the Queen has ordered a doctor named Cornelius to prepare her a deadly poison, which she claims will be used for scientific purposes, on small animals and the like. Cornelius is suspicious of her, however, and tells the audience that he has given her not a poison, but a sleeping potion that will effect the appearance of death. When he has gone, the Queen confirms his suspicions of her by giving the "poison" to Pisanio and telling him that it is a soothing medicine. She hopes that he will take it and die: Pisanio, as Posthumus's servant, supports and champions his master, and when he is dead, it will be easier to convince Imogen to marry Cloten. Thus, we see that her earlier, honeyed words to Imogen and Posthumus were indeed nothing but lies, just as Imogen thought, concealing her malicious and selfish purposes.
Meanwhile, Iachimo arrives from Italy and gives Imogen a letter from Posthumus. He immediately begins to compliment her grace and beauty, and when she asks about her exiled husband, Iachimo tells her that Posthumus has all but forgotten her, and is enjoying himself--and, he implies, enjoying other women-- while in Italy. Imogen is horrified, and Iachimo attempts to play upon her injured feelings by suggesting that she might revenge herself on the unfaithful Posthumus by being unfaithful herself--with him, naturally. The princess, taken aback, rebuffs him, and declares that she does not believe his malicious stories about her husband's conduct. Iachimo quickly admits that it was all a lie and says that he only attempted to seduce her because he loves Posthumus so much and wanted to test Imogen to make certain that he had a faithful and worthy wife. After begging her pardon profusely, he offers to carry her letters to her husband, and he then asks her permission to store a large trunk in her chambers--he claims that it contains his most valued possessions--and she grants his request.
Meanwhile, Cloten is behaving typically, complaining about his poor luck in a game of bowling, while the two gentlemen who attend on him make fun of him behind his back. When he has gone, one of them remarks on how peculiar it is that such a crafty mother should have borne such a foolish son, and he then expresses his sympathy for Imogen's predicament and hopes that she will weather her current predicament and find happiness with her husband.
That night, when Imogen goes to bed, Iachimo's trunk sits stored in her room. After she has fallen asleep, the trunk opens and Iachimo himself slips out. He watches her as she sleeps and then makes careful note of all the furnishings in her bedchamber, as well as a particular birthmark on her left breast. Then, he slips from her wrist the bracelet that Posthumus gave to her and slips back into the trunk, planning to present the item of jewelry, as well as his new familiarity with her chamber, as evidence of a successful seduction.
A number of critics have remarked on the way Shakespeare, in this late play, recycles elements from a number of his earlier works, rendering Cymbeline a kind of compendium of Shakespearean plot devices. The pairing of Cymbeline and Imogen--a tyrannical father and a virtuous, unfairly treated daughter-- clearly parallels the Lear-Cordelia relationship in King Lear, while Iachimo plays a dwarfed version of Iago to Posthumus's unconvincing rendition of the Othello character. The idea of the sleeping draught that effects the appearance of death parallels a similar potion in Romeo and Juliet. In the tragedies, however, just one of these situations suffices to call down destruction, while in Cymbeline, the characters show a remarkable ability to avoid the snares that Shakespeare strews liberally throughout the plot.
The plot moves along briskly in these scenes--Iachimo's journey from Italy to Britain seems to have taken no time at all--and Iachimo, thus, goes to work on Imogen immediately. The princess displays a remarkable strength of character in her conversations with the Italian rogue, and her refusal to doubt Posthumus's constancy makes a sharp contrast with her husband's ready jealousy later on. But the scene really belongs to Iachimo, who displays a remarkable adaptability: His cheerfully brazen attempt at seduction having failed, he quickly shifts gears and makes the equally brazen claim that he was only testing Imogen. He then launches into a ridiculously overblown account of Posthumus' virtue. "He sits 'mongst men like a descended god (I.vi.169)," Iachimo declares, keeping a straight face. Thus, the key to his character becomes clear: He is an actor, constantly performing, though his deceptions can be somewhat amateurish. We are immediately struck by the obvious contrast between this man and his fellow Italian villain, Othello's Iago. There is nothing amateurish about Iago, who derives his malicious delight not from the acting itself, but from the havoc this performance wreaks.