In the original legend and in the earliest melodramas and plays, Sweeney Todd has no wife or backstory and is the primary villain of the stories he appears in.
Mistakenly believing her to be dead, Barker undertakes a long string of murders, with the ultimate goal of killing Turpin in order to avenge the destruction of his family.
When Benjamin Barker, under the alias of "Sweeney Todd", returns years later, Mrs. Lovett, who was in love with him, leads him to believe that Lucy is dead so that she could have him to herself.
Lucy shows evident distaste for Mrs. Lovett, calling her a witch and constantly hanging around her meat pie shop.
Downstairs, after Todd has killed Judge Turpin, Lovett recognizes Lucy's body and scrambles to get rid of her.
Stricken with remorse, Todd holds Lucy's body and allows Tobias Ragg to cut his throat, leaving them dead in each other's arms.