The ABC drama focuses on Emily (Emily VanCamp), who is looking for revenge on the people who destroyed her father.
However, Kelley told the New York Post that Emily is not after a quick fix.
"For Emily, revenge does not have a finite end," he said. "Her idea of revenge is to make these people suffer as deeply and as long as she and her father suffered.
"She doesn't want to push Conrad over a cliff or run Victoria over with a car. She wants them to suffer every day. So the longer she can draw this out, that's her version of a successful revenge, and that's what will sustain the series, continuing her torment of the family."
Kelley also teased that some of the other characters may be looking for revenge, saying: "You will find that revenge is a permeating theme on the show. It's not just referring to Emily's storyline, but everybody will be wronged and everybody will have their opportunity at it."
He added that revenge might not work out well for everyone.
"The only way out of revenge is either demise or forgiveness," Kelley hinted. "So that's where we're ultimately headed."
Revenge airs on Wednesdays at 10/9c on ABC.
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