Lucia is a young woman with the bad luck of being born in the 17th century. She loves Edgardo, but his father did Lucia's family dirty in the old days, so now the son is persona non grata. Lucia's brother Enrico is broke and has found a suitable rich man, Arturo, for Lucia to marry to set the family finances back in order. Enrico finds out Lucia loves someone else, is angered that it might ruin his plans and proceeds to strong-arm Lucia into marrying Arturo — the sooner the better.

Naturally, this unleashes every kind of bad side effect, ending in an ugly scene of carnage, but not before there is a peerlessly beautiful sextet and the best mad scene in opera. And Enrico is still broke.