Psychologist Serena unknowingly has a one-night stand with Eleanor, who turns out to be her new stepsister after Serena's mother marries into Eleanor's family. Eleanor blackmails Serena into obeying her in risky situations, and the two gradually fall for each other amid moral turmoil. When Serena's ex-boyfriend discovers their relationship and extorts Eleanor, Eleanor pretends to be heartless and drives Serena away to protect her. Serena leaves heartbroken, becomes a renowned psychologist, and secretly treats Eleanor's psychological illness for years. They reunite six years later at a medical forum. Eleanor uncovers the truth and confines Serena, eventually revealing that she pushed her away to shield her. The two finally confess their true feelings and reconcile.
