Aemilia Bassano Lanier is beautiful and accomplished, but her societal conformity ends there. She frequently cross-dresses to escape her loveless marriage and gain freedoms only men enjoy, but a chance encounter with a ragged, little-known poet named Shakespeare changes everything. They leave plague-ridden London for Italy, where they begin secretly writing comedies. Their Italian idyll, though, cannot last and their collaborative affair comes to a devastating end. Will gains fame and fortune for their plays back in London and years later publishes the sonnets mocking his former muse. Not one to stand by in humiliation, Aemilia takes up her own pen in her defense and in defense of all women. The Dark Lady's Mask gives voice to a real Renaissance woman.