Agatha Clay is a young woman with a mysterious past. She lives in a world complicated by Sparks (think mad scientists with the ability to create devices and living things that bend or break the known laws of science) and ruled by Baron Wulfenbach, a Spark who conquered Europe to stop the chaos. Agatha's doesn't know her origin or about her imminent Sparkhood. When a mugging and theft allows her talents to break loose without warning, all hell begins to break loose, too.
Girl Genius is beautifully drawn and wonderfully manic. Its characters are human, animal, robotic (called Clanks), and artificial biological constructs. The huge story includes Agatha, the Baron and his son Gilgamesh (himself a developing spark), the King of Cats, Jagermonsters, pirates, the most fearsome nanny in the known universe, a traveling circus, Translyvania Polygnostic University, various monsters, and Punch and Judy. The backstory underlying it is fascinating, imaginative, and enormously detailed. The villains are not totally evil, and the good have their dark sides, but don't take any of it too seriously. This is comedy that is both broad and pointed, and it works beautifully.
This comic is a whacko masterpiece of adventure, romance, and discovery. After fifty years of reading all sorts of comics, this is now my all-time favorite.