On this week's episode of Elementary…
A serial killer named Ennis is sent to a hospital to donate a kidney to his dying sister.
Ennis escapes, leaving Holmes and an FBI profiler named Kathryn Drummond to hunt him down, despite his new M.O.
Holmes had a relationship with Kathryn, who also happened to capture Ennis.
Kathryn lied about Ennis being sexually abused in her book, causing Ennis' parents to kill themselves.
Ennis ropes his sister in his revenge ploy and although they cut Kathryn, she survives.
Holmes figures out Ennis' location through radio signals, and tests Ennis in order to determine if he could be a changed man.
Holmes captures Ennis.
Watson plans on finding a new place, especially after she finds out her apartment is being used to film porn.