Charles Darwin left behind more than 15,000 letters sent or received over his lifetime, and the Darwin Correspondence Project has spent decades tracking them down, transcribing them, and publishing them in full. This film comes out of that project's "Darwin & Gender" research strand, using the archive to look specifically at the women in Darwin's orbit: family, friends, and correspondents whose letters shaped his thinking alongside the more famous exchanges with fellow scientists. About half the original letters sit in the Darwin archive at Cambridge University Library, with the rest scattered across archives and private collections worldwide, and new ones still turn up most years. The Correspondence of Charles Darwin now runs to 20 published volumes, and over 7,500 letters are free to read on the project's website. Rather than a conventional biography, the film works like an annotated reading of the archive, using the letters themselves to argue that Darwin's science was never a solitary undertaking.