Dissembling courtesy! How fine this tyrant Can tickle where she wounds! (1.1.98-99)
Don't say you weren't warned: Imogen tells us upfront that the Queen is up to no good. It's a shame her dad can't see his wife's deception. Everyone else seems to detect it within seconds of meeting her. Imogen knows her stepmother is wicked, even if she pretends not to be. Why can't Cymbeline himself see this? Is he blinded by love (or lust)?
CORNELIUS I do not like her. She doth think she has Strange lingering poisons. I do know her spirit, And will not trust one of her malice with A drug of such damned nature. […] She is fooled With a most false effect, and I the truer So to be false with her. (1.5.40-43; 49-51)
The Queen is so confident about her smarts and her ability to lie and manipulate that she fails to consider the possibility that the doctor might outsmart her and foil her evil plans. Hey, Cornelius went to med school: he knows the Queen is lying about why she needs a potion. But he also knows he can't trust anyone with that information. He'll just have to lie low and watch out.
IACHIMO Be not angry, Most mighty princess, that I have adventured To try your taking a false report, which hath Honored with confirmation your great judgment In the election of a sir so rare, Which you know cannot err. The love I bear him Made me to fan you thus, but the gods made you, Unlike all others, chaffless. (1.7.198-205)
Irony alert: Iachimo weasels his way into Imogen's trust by lying to her and then lying some more. Even as he blabbers on about trust, we know he's lying. This two-faced villain won't lose a bet, even if it means lying his face off. He even seems to enjoy lying, maybe because he thinks it shows how much smarter he is than everyone else. Do you think he actually is that much smarter than everyone else?
IACHIMO She stripped it from her arm. I see her yet. Her pretty action did outsell her gift And yet enriched it too. She gave it me and said she prized it once. (2.4.128-131)
Posthumus falls for Iachimo's trick hook, line, and sinker. Once the bracelet is shown, all bets are off. Posthumus knows how important that bracelet is, so he believes Iachimo. We'd also like to point out how malicious Iachimo is when delivering the (fake) news: he adds a stinger by saying Imogen prized it—or Posthumus—once but doesn't anymore. What's the point of this? Does he just want to be "better" than Posthumus? Why bother with all of this stuff?
POSTHUMUS ...be it lying, note it, The woman's; flattering, hers; deceiving, hers; Lust and rank thoughts, hers, hers; revenges, hers; Ambitions, covetings, change of prides, disdain, Nice longing, slanders, mutability, All faults that have a name, nay, that hell knows, Why, hers, in part, or all, but rather, all. (2.5.23-29)
It's all women's fault, Posthumus claims. He's livid at his wife for betraying him, but he takes it to the next level when he rants and rages at all womankind. The ladies are deceitful, fickle, lustful, and disdainful. Every lie comes from woman. Umm... apparently, Posthumus has never met Iachimo. Oh, wait, he has. Dramatic irony, anyone?
IMOGEN Men's vows are women's traitors! All good seeming, By thy revolt, O husband, shall be thought Put on for villainy, not born where 't grows, But worn a bait for ladies. (3.4.56-59)
Imogen loves Posthumus, but when she reads his letter accusing her of all kinds of nasty things, she delivers a rant herself. Men seem good but really just lay out bait to trap women. She's sort of right, but she's sort of wrong: we've seen how that nasty Queen laid her own trap for Cymbeline. If people could just cool down a little, they might see that men and women can be equally nice and equally nasty to each other.
IMOGEN Pisanio, All curses madded Hecuba gave the Greeks, And mine to boot, be darted on thee! Thou, Conspired with that irregulous devil Cloten, Hast here cut off my lord. To write and read Be henceforth treacherous. Damned Pisanio Hath with his forgèd letters—damned Pisanio— (4.2.385-391)
As if being wrongfully accursed of adultery weren't enough, now Imogen is poisoned. But we're more interested in whom she blames: she thinks Pisanio has been in on it with Cloten the whole time. He's a filthy, no good liar, right? Not right. The irony is that Pisanio is one of the only characters who is honest with her the entire time. She's acting a lot like Posthumus, who suspects Imogen instead of Iachimo when things seem to go wrong.
PISANIO Wherein I am false I am honest; not true, to be true. These present wars shall find I love my country, Even to the note o' th' King, or I'll fall in them. All other doubts, by time let them be cleared. Fortune brings in some boats that are not steered. (4.3.50-54)
Poor Pisanio: he's accused of all kinds of deception, and yet he's the most trustworthy of the lot. He says he trusts that he will clear his name. No one likes to be called a liar, but Pisanio takes it in his stride; he knows the truth will set him free.
CORNELIUS Your daughter, whom she bore in hand to love With such integrity, she did confess Was as a scorpion to her sight, whose life, But that her flight prevented it, she had Ta'en off by poison. (5.5.52-56)
Don't kill the messenger: that's what Cornelius is thinking when he delivers a laundry list of wicked deeds from the Queen to Cymbeline. Here, he uncovers all the Queen's lies. We knew she was mean, but killing the king and princess so that your son can reign? That's a whole new level of deception.
IACHIMO That I returned with similar proof enough To make the noble Leonatus mad, By wounding his belief in her renown With tokens thus and thus; averting notes Of chamber-hanging, pictures, this her bracelet,— O, cunning how I got it!—nay, some marks Of secret on her person, that he could not But think her bond of chastity quite cracked, (5.5.236-243)
Finally the truth comes out. Iachimo gives all the deets about his totally fictional tryst with Imogen. In a play with so many lies, the final scene is pretty much entirely devoted to setting the record straight. Iachimo, we've got to say, has a lot to answer for, since he and the Queen have been the worst offenders.