Cecilia Kass is trapped in a violent, controlling relationship with wealthy optics engineer Adrian Griffin. Fearful for her life, she executes a harrowing midnight escape with the help of her sister, Emily. After her escape, she learns of Adrian's apparent suicide and his will bequeathing her a substantial portion of his vast fortune. However, the conditions of the will stipulate that she must be mentally competent to receive the inheritance. Cecilia suspects Adrian's death is a hoax and that he has found a way to become invisible to continue tormenting her, controlling her life without anyone else noticing.

As strange occurrences begin to unfold, Cecilia's sanity is questioned by those around her, including her childhood friend, James, and his teenage daughter, Sydney. Despite her pleas, no one believes her claims that she is being hunted by someone nobody can see. The harassment escalates, with Adrian always seemingly one step ahead, using his invisibility to manipulate her environment and frame her for outrageous acts. Cut off from support and increasingly isolated, Cecilia is driven to the edge as she tries to prove that she's being terrorized by an unseen adversary.