Aurelia Davenport considers herself the ideal Victorian housewife. She's had an excellent upbringing and education. She is dutiful to her husband, a captain in Her Majesty's Royal Navy. She is well respected in local and London society.
And she hates it. Respect isn't friendship or companionship. Her marriage is only one of convenience for her secretly gay husband, leaving her childless. Which only makes her a disappointment to her overbearing mother. Aurelia is completely alone.
Until she meets the mysterious and literally other-worldly Marcus, an alien from another world. He and his living ship are stranded on Earth and he needs her to help him get it back and save the world. He promises her excitement, exploration, and worlds she never could imagine. He reveals to her a terrible plot, hatched by a madman, to murder the royal family and destroy civilization.
She faces a choice. She can stay in the horrible life that's been laid out for her, knowing that to do so will risk the loss of her family, her well-being, and her future. Or risk it all for once chance at adventure, and to save the world, knowing she could lose everything and live destitute and penniless for the rest of her days. Assuming any of them survive the experience.