Let's say you're a young woman of good family in the early nineteenth century. You're grieving your mother's recent death, and your family is on shaky political ground. You've met a dude named Edgardo who looks like an Oompa-Loompa but sings like an angel, and you've been secretly confessing your love to each other despite the fact that your brother Enrico considers him your family's greatest enemy.
But your brother has Edgardo sent into exile and is pressuring you to marry some other dude named Arturo for political reasons. (He seems okay, but you're promised to Edgardo!) Your brother even has a letter from Edgardo (a forgery) saying he's already betrayed you. Enrico threatens to curse you forever if you don't make the marriage to save his life.
So you reluctantly agree. And then! Edgardo bursts in on your wedding day, just after you have signed the contract, and curses you anways! You can't win! What on earth do you do next?
If you're Lucia, you go brilliantly, spectacularly insane -- kill your brand-new husband, strip off your bloody wedding gown in front of a stage full of horrified guests, and slit your own wrists while the audience gasps in shock.
It's almost a proto-feminist narrative, in the way it depicts the ruin of one woman's life as a catastrophic failure on the part of the men who love her. Neither Edgardo nor Enrico are particularly heroic in this story. They're childish and stubborn and it is clear they let Lucia down.
And then Edgardo stabs himself with a stiletto when he learns of Lucia's death. So we as an audience forgive him. The brother stays offstage and goes unpunished, which is disappointing, though presumably his life is pretty near ruined by the whole thing. Take that, you selfish bastard.
The staging was simply luscious. The costumes! And the set! Why stop at one spiral staircase when you can have two?
Decadence, thy name is two spiral staircases.