In a feud between the Scottish families of Ravenswood and Lammermoor, Enrico (Lord Henry Ashton of Lammermoor) has gained the upper hand over Edgardo (Edgar of Ravenswood), murdering his kinsmen and usurping his estates.

By the time of the opera's action, in the late 17th century, Enrico's fortunes have begun to wane; in political disfavor, he stakes all on uniting his family with that of Arturo (Laird of Bucklaw), whom he means to force his sister, Lucia, to marry.