Struggling writer Lee Israel finds herself frustrated with her stagnant career and financial woes, unable to get published as she falls out of step with current tastes. She is an abrasive, cantankerous soul who prefers the company of her cat and the drink to that of people, often pushing away even those who attempt to get close to her. After being fired from her copy editing job, Lee stumbles upon a lucrative scheme while researching for a biography on Fanny Brice. She discovers a letter included in a library archive and decides to pilfer it for a small profit.

Sensing an opportunity in the collectors' market for literary memorabilia, Lee initiates a cunning plan to forge letters by deceased writers and playwrights. Using her talent for mimicry and her background as a biographer, she is able to produce convincing fakes, embellishing them with personal details to elevate their value. As her confidence grows, Lee enlists the help of her only friend, Jack Hock, a boisterous and equally down-on-his-luck who becomes her partner in crime. Together, they expand the operation, but as the stakes rise, so does the scrutiny from buyers and federal authorities, threatening the fragile thread of success Lee has spun from her web of deceit.