An unnamed narrator is caught in heavy rain while lost in the Welsh countryside. Coming across a decrepit-looking tower, he sees a friendly old woman pop her head out through a hole in the side. Soon, he is beckoned in to wait out the storm. Inside, he is surprised to discover that the rough-looking tower is furnished like a comfortable home.

As he looks around, his curiosity is immediately piqued by a portrait that stands out from its surroundings. Labeled "The Invisible Girl," it depicts a pretty, contented young girl reading a book with a mandolin at her feet. Inquiring about the portrait, he comes to learn the story of the girl, the tower itself, and the old woman's connection to the property.

When a traveler arrives in a nearby village some years earlier in search of a ride across the water, the old woman tells him, the weather is ominous. Still, two villagers step forward and accept—a father, in need of the money, and the old woman's son, in need of the thrill. The villagers recognize the traveler as Henry Vernon, the young son of Sir Peter Vernon, who keeps an estate nearby.

As the three men embark on their journey, the two hired men are optimistic about the voyage. Soon, the water becomes rough—they fight extreme wind and unruly waves, and struggle to see the shoreline in the dark. When a light appears in the distance, the younger sailor tells Henry that it is a beacon lit by "The Invisible Girl," a reclusive young woman who, he has heard, lost her sweetheart to the sea.

When they finally reach the shore, guided by the beacon, the boat is severely damaged. Finding the abandoned tower, they take shelter inside. As the two hired men sleep, Henry Vernon instead fixates on the source of his overpowering grief—his heartbreak over his lost love, Rosina.

Rosina, an orphan, was raised alongside Henry as a ward of his father, Sir Peter. Sir Peter was loving and generous with the children, but he was also extremely volatile—his temper was severe, and Rosina's fear of upsetting him led her to extreme obedience and agreeability in his presence. As they grew up, Henry and Rosina developed a romantic bond. Content to wait until they were old enough to marry, they hid their love from Sir Peter to avoid inciting his temper.

When Mrs. Bainbridge, Sir Peter's widowed sister, arrived—shortly after, the narrator notes, killing her own husband—the two were discovered. Unlike Sir Peter, Mrs. Bainbridge's cruelty did not alternate with kindness. Instead, she was determined to seek out new targets for her antagonism. She discovered the bond between Henry and Rosina and informed Sir Peter immediately.

To separate the two, Sir Peter sent Henry abroad and sequestered Rosina in order to inhibit all communication between the two. When Mrs. Bainbridge intercepted a letter Rosina had attempted to send Henry in secret, Sir Peter was furious. He cast her out of the house in anger, and she wandered off into the night.

After she had been gone for some time, Sir Peter began to worry—his intention was only to punish the girl, and now she seemed to have disappeared. Before long, he came to believe the worst: Rosina, already weak upon her exile, had succumbed to the harsh elements and died.

Disconsolate, a grieving Henry returned home to Wales to search for Rosina's remains. It was in this state that he arrived in the village to seek passage across the water and hired the two local men for their tumultuous boat journey. As he sits in the...