My name is Nell Okafor. I am thirty-one, and for twelve years I have been the wardrobe mistress of the Aurelia Theatre, a cream marble opera house the town forgot to close. In a locked vault behind the stage hang four hundred costumes, some older than my grandmother.

Old Mr. Fenn, who owns the building and has owned it for fifty years, was taken to a clinic by the sea in March. Before the ambulance doors closed he pressed the vault key into my palm and said, very quietly, that nobody opens it but me. He also said: keep the dog fed and keep the doors unlocked.

The dog is Bram. Bram is a grey Great Dane who stands as tall as my shoulder, weighs about a hundred and sixty pounds, and has never once barked at a stranger. He spends his days on the foyer’s cool marble floor. He followed Mr. Fenn everywhere, and with Mr. Fenn gone, he followed me.

Six weeks later, on a Tuesday, Mr. Fenn’s niece Cordelia Voss arrived with two men in hard hats. Pale gold satin blouse, a silver-and-auburn chignon, a voice like a closing door. The men measured the walls. Cordelia walked straight to me and held out her hand.

“The theatre is sold,” she said. “The vault contents go to the developer with the building. Give me the key. You have until noon.”

I told her I would hand it over the day Mr. Fenn asked me to. That was all. She smiled, which frightened me more than shouting would have, and she took my elbow and walked me across the upper landing to the top of the great curved staircase.

I was in my smock, cream cotton, with pins still stuck in the hem, and barefoot, because I had spent the morning kneeling on the stage. My hand found the dark banister. Below us the foyer was silent and bright, the arched window throwing a long square of daylight across the marble. I was crying and I hated that she could see it.

“The key, Nell.”

“No.”

Her two palms landed flat between my shoulder blades. My feet left the step. I remember the banister sliding out of my fingers and the whole cream hall tipping sideways, and then the last steps rushing up, and then the floor, cold and hard and glossy. I slid. I came to rest on my side with my cheek against the marble and no air in my chest at all.

I could see Cordelia at the top of the stairs. She was very small from down there. She stood with her arms hanging and did not come down.

I did not try to get up. I could not. I lay there and the tears ran sideways across my face, and I thought about the vault, and Mr. Fenn’s hand closing my fingers around the key.

Then the tall front doors banged open so hard they struck the walls. White daylight poured in, and with it came Bram, running, which I had not seen him do in three years. His claws scrabbled on the marble, he skidded, and he planted himself over me like a wall, all hundred and sixty pounds of him, and lowered his great grey head until his muzzle rested against my shoulder. He was shaking. So was I.

Cordelia had come down three steps. Now she stopped. Both her hands went to her chest, crossed over the pale gold silk, and her mouth fell open, and for the first time since she walked into the foyer she looked like a person who had not planned what happened next.

Because behind Bram, in the doorway, leaning on a cane with a taxi still idling at the curb, stood Mr. Fenn.

He had discharged himself from the clinic that morning. He had also, it turned out, rung the theatre’s caretaker from the taxi and told him to open the courtyard gate and let the dog go, because Bram, who could hear that taxi from two streets away, would know what to do.

Mr. Fenn crossed the marble one slow step at a time, lowered himself into the foyer’s little gilt chair, and took my hand. He did not look at his niece. “Are you hurt, Nell?” he asked. I said I did not think so. A paramedic said later that I had a bruised hip and a sprained wrist.

Then he looked up the staircase. “The theatre was never mine to sell, Cordelia,” he said. “I put it into the Aurelia Costume Trust in April. Nell holds the only key, and the trustees are the people who have worked here. I signed the last page from my hospital bed with a nurse as a witness. Your developer has been buying a building that nobody owns.”

Cordelia said nothing. The two men in hard hats picked up their tape measures, apologized to me, and left. She followed them out, down the steps, without her handbag. Bram watched her go and then lay down on the marble beside me with a heavy sigh, and put his chin across my ankles.

The Aurelia opens again in October. The costumes are all still in the vault, and I still hold the only key. And every morning at ten, if you push the tall front doors open, you will find a grey dog lying in the daylight on the cool marble, waiting for someone to come through.