Cassandra Lightman grew up making trinkets and toys. She was on her way to inventing a "flying machine" when she was committed to a sanatorium for hysteria. That's where Dr. Timothy Brown found Sandra and saw her promising intelligence. After Sandra shows Dr. Brown how to cure hysteria in women, she begins to work under him in his medical practice. Since Sandra cannot practice medicine and has no support from her family, she must carry on her position in secret. She goes into Dr. Brown's office through the back door, speaking to no one, and always covering her face. Sandra soon meets Bedelia Morten, one of her patients behind the red curtain. Bedelia Morten is an upper class wife with a banker husband and three children of her own. She suffers from insomnia and nightmares, which leads her to seek out Dr. Brown's practice. Though Bedelia is initially skeptical of Sandra's skill, she soon learns to appreciate Sandra's talent and company. When their relationship becomes too close, Sandra is encouraged by Dr. Brown to invent a "stand-in" for herself. Sandra goes back to her experimental roots and visits her idol-inventor Marlin Manchester. Sandra works many long nights in hopes of creating the first steam-powered vibrator. When Sandra's invention takes off, she is forced to reconsider her role both in and out of the examination room, her future, and who she wants by her side.