Most good stories start with a fundamental list of ingredients: the initial situation, conflict, complication, climax, suspense, denouement, and conclusion. Great writers sometimes shake up the recipe and add some spice.
Exposition (Initial Situation): You Know What They Say about Evil Stepmothers
Imogen's evil stepmother pretends to be her friend and a calm counselor to the king, when she is really whipping up potions and planning their murders behind their backs (or paying people to at least.) The Queen desperately wants her son, Cloten to marry Imogen and become king of Britain. Imogen's new hubby Posthumus is banished along with her hopes and dreams for a happy life. The lovebirds give each other tokens—a bracelet for her, a ring for him—and promise to keep them forever.
Rising Action (Conflict, Complication): Challenge Accepted
Posthumus bets Iachimo that he won't be able to score with his honey, but he didn't know Iachimo would lie, cheat, and steal to get the job done. Imogen proves her faithfulness, but Iachimo takes her precious bracelet and a gander at things that aren't his.
Climax (Crisis, Turning Point): This Means War
Posthumus believes Imogen is a big fat cheater and orders Pisanio to kill her. She dresses as a boy (Fidele) and flits off to Wales to find a ride to Rome. Meanwhile, Cloten treks out to Wales as well in hopes of killing Posthumus and taking Imogen for himself whether she likes it or not.
Falling Action: Cross My Heart and Hope to Die
Imogen has made some new friends in Wales, but little does she know that Guiderius and Arviragus are her long-lost, kidnapped brothers. She takes a medicine from the Queen but it's actually poison and she dies—only briefly—and wakes up again. But it's long enough for her new friends to mourn her. The good news is they've managed to kill Cloten when he happened upon them while hunting. No loss there! Meanwhile, Rome is invading Britain for some of the Queen's gutsy decisions.
Resolution (Denouement): Family Reunion at the Palace
Britain defeats Rome thanks to Belarius, Guiderius, Arviragus, and Posthumus. After they are knighted or released from prison, it's a whirlwind of family reunions as Fidele reveals herself as Imogen. Iachimo comes clean about his lies and apologizes. Then, Belarius fesses up to kidnapping Guiderius and Arviragus years earlier. Cymbeline and his family are together again at last!