Shakespeare begins his play Cymbeline in the middle of a mess at the court of the title character, a king in Britain. His wife had died long ago, leaving two toddler boys and an infant girl, Imogen. Cymbeline had banished Belarius one of his most loyal noblemen, and as he fled, Belarius had convinced the children's nurse to kidnap the two boys and go with him to live in the woods, where a few scenes into the play, we see them -- now adult men -- in their cave.
At the start of the play, Imogen is a young woman, and has just eloped with a visitor to court, Leonatus Posthumus, a Roman. We quickly learn that Cymbeline's second wife was beautiful and manipulative in a very evil way. Her aptly named son Cloten (rhymes with Rotten) was a very dumb clod who could hardly speak prose and virtually never spoke the native iambic pentameter of the other characters. Cloten and his mother had had a plan: he would marry Imogen and take over the kingdom. Obviously, Imogen's love marriage thwarted that, and they were angry and vengeful. The Queen can make Cymbeline do anything: she has him banish Posthumus.
Next we have a tricky part of the plot. Leonatus Posthumus brags about Imogen to the wrong people, who wager that she can be led astray. One of them has himself smuggled into her bedroom in a chest, and while she sleeps he memorizes all its secrets and steals the bracelet that her husband had given her. Wronged and innocent, she is cast out of court and soon assumes the disguise of a boy.
Now we are set up for a series of wanderings in the woods and finally a long series of recognition scenes, as fathers and children and husbands and wives are reunited. But only the good ones: Cloten, on his way to rape Imogen and kill Posthumus, is beheaded by one of her unrecognized brothers, and Cymbeline's Queen dies, repenting all her evil deeds. Spirits and Roman gods appear in dreams to Posthumus, predicting justice and harmony. And the predictions come true as Cymbeline emerges as a more kingly figure, no longer just henpecked and stupified.
Why does it read so well? Shakespeare made it all work. The interactions, though improbable, are very dramatic, and the poetry is as impressive as any. Imponderable, I think.