Older women often feel invisible, but sometimes that's their secret weapon. Billie, Mary Alice, Helen and Natalie have worked for the Museum, an elite network of assassins, for forty years. But now their talents are considered old-school and no one appreciates their real-world resourcefulness in an age of technology. When the foursome is sent on an all-expenses-paid trip to mark their retirement, they are targeted by one of their own. Only the Board, the top-level members of the Museum, can order the termination of field agents, and the women realise they've been marked for death. To get out alive they have to turn against their own organization, relying on experience and each other to get the job done, knowing that working together is the secret to their survival. They're about to teach the Board what it really means to be a woman - and a killer - of a certain age.