That such a crafty devil as is his mother
Should yield the world this ass!
Imogen has agreed to look after a trunk for Iachimo, rather naively, if I may be so bold as to say so. Sure enough, when she drifts off to sleep he pops out of the trunk, creeps around her bedroom for a while, takes her bracelet from her arm (sound sleeper, that Imogen) and disappears back into the trunk.
Next up, Cloten, the king's stepson, tries to put the moves on Imogen, but she's not having any of that. Then Iachimo manages to convince Posthumus that he has had his way with the alleged tramp Imogen. Some of Posthumus's pals try to encourage him not to be so easily swayed but he's not having any of that.