Fifteen years ago, Caroline's husband accidentally murdered a prostitute, panicked and disposed of her body. Luther tracked him down and was utterly brutal in the way in which he put him away, so he killed himself. In the process, Caroline lost her wealth, her health, her friends and her happiness. Her life was hauled over the coals by the tabloids and her daughter went off the rails.
She trusted in Luther to help her, but ended up as a victim on the sideline of his campaign for justice. As far as Caroline's concerned, Luther destroyed her life and her daughter Jenny's life. Luther owes her big time.