After she goes into the wilderness disguised as a boy, Imogen gets lost, despite receiving directions from a pair of beggars. As a result, she spends two days sleeping on the ground and trying not to succumb to hunger. When she comes across the cave of Belarius, she goes inside for shelter, though with her sword drawn as a precaution.
By a stroke of luck (or perhaps fate), the cave is the home of three shepherds: Belarius and his adopted sons, Guiderius and Arviragus. Unbeknownst to Imogen, the two younger men are her long-lost brothers, taken from the royal court by Belarius, himself a disgraced nobleman, as revenge upon her father, Cymbeline, for banishing him unjustly. Belarius's situation parallels Imogen's in that she too was accused of a crime she did not commit and is being unjustly punished for it.
Once they note her presence, the trio takes Imogen into their care (though she introduces herself to them as Fidele, both to disguise her gender and to subtly emphasize her faithfulness to her husband). This allows Imogen a respite from her fruitless wandering in the wilderness and allows her to form a relationship with family members she never knew, slowly setting up the reconciliation at the play's end.