Let Her Out follows Helen| a bike courier who suffers a traumatic accident. As she recovers| she begins to experience strange episodic-black outs| hallucinations| and night terrors-that lead her to discover that she has a tumor| a benign growth that is the remnants of a "vanishing twin" absorbed in utero. Over time| the tumor manifests itself as the dark and demented version of a stranger. As Helen's emotional and psychological state begins to deteriorate further and further| she begins to act out in psychotic episodes that are influenced by her evil twin - making her a danger to herself and her best friend| Molly.