Cathy Martin, leading a perfect life as a married teacher, unexpectedly encounters her brother’s murderer, Michael McAllister, in a supermarket. Consumed by the encounter, she begins stalking McAllister on social media, leading to an escalating obsession.

Creating a fake online persona, she infiltrates his life, flirting with him, befriending his wife, and even breaking into his house. With a fragile personality already disturbed by buried trauma, Cathy’s actions become increasingly dangerous, driven by a desire to destroy McAllister’s happy existence.