The sea mist curled around the granite island like a cat seeking warmth. Edgar Preston stood at the edge of the overgrown garden and watched the white roses bloom behind the broken greenhouse glass, their petals thick and waxy and perfect, their thorns black and sharp and real. He had been on the island for five days. He had not slept in four.

The sanatorium was a Victorian relic — high ceilings, narrow corridors, rooms with no windows, a chapel with a locked confession booth where a nun named Sister Rachel had vanished three nights ago. The door had been locked from the inside. The window had been sealed with paint. Sister Rachel had simply ceased to be in the booth.

Edgar was not a detective. He was a former Harvard psychology lecturer who had become obsessed with trauma memory research and had lost his mind in the process. Or perhaps he had found it. The distinction was one he no longer trusted.

His wife, Isabella, had died two years ago. Of puerperal fever. That was what the doctor had said. But Edgar's memory of her death was unstable — sometimes she had died in a fire, her dress black with soot, her face a mask of ash. Sometimes she had drowned, water pouring from her mouth, her eyes wide and wet and accusing. Sometimes she had burned and drowned at the same time, smoke and water mixing in the air like a nightmare made physical.

He found Sister Rachel's cipher on the chapel floor, tucked beneath the confession booth's door:

THE RULE OF THIRTEEN I AM 47 THEY WERE ONCE 80 PLUS YOU ARE 3 WE ARE 4 BUT WHO IS 67?

Edgar worked on it in the sanatorium's library, a room lined with leather-bound books that smelled of mildew and old ink. He tried letter-to-number. He tried counting syllables. He tried every system he had studied in his years as a psychology lecturer. Nothing worked.

On the fifth night, he dreamed of Isabella.

She stood in the garden, wearing a dress of white lace, and the sea mist curled around her ankles like a lover's fingers. She turned to him and her face was beautiful and broken and burning and drowning all at once, and she said: "I am here. You are here. He is here. You cannot leave. The garden is a mirror. Look at it."

Edgar woke screaming. The sanatorium's walls seemed to lean inward, closing around him like the ribs of some vast and ancient creature. He lit a candle and went to the library, and there, by the flickering light, he saw it.

Thirteen. Not four. I-S-A-B-E-L-L-A had eight letters. I-S-A-B-E-L-L-A-P-R-E-S-T-O-N had twenty letters. But the name in the cipher was not Isabella's. It was the nun's. S-I-S-T-E-R-R-A-C-H-E-L had thirteen letters.

The cipher was not about a missing nun. It was about a missing wife.

He worked through the night. The numbers mapped to something deeper than letters — they mapped to memories. Forty-seven was the number of days Isabella had been sick before she died. Eighty was the number of letters in their wedding vows. Three was the number of times Edgar had held her hand as she died. Four was the number of seasons they had been married.

And sixty-seven?

Sixty-seven was the number of mirrors in the sanatorium. He had counted them himself — in the corridors, in the bedrooms, in the chapel, in the library. Sixty-seven mirrors, each one reflecting a different fragment of a different person's broken mind.

Edgar stood in the chapel at dawn, the decoded cipher in his hand, and understood. Sister Rachel had not disappeared. She was a reflection. Isabella was a reflection. He was a reflection. The island was a mirror, and every patient was a fragment of his own shattered memory, and the cipher was not a code to be solved but a mirror to be looked into.

He walked to the garden. The white roses bloomed behind the broken glass. The sea mist curled around his ankles. He looked at his reflection in a puddle of seawater. His face was Isabella's face. Isabella's face was his face. The boundary between them had dissolved — like sea mist, like memory, like truth.

Edgar Preston closed his eyes and let the mist take him.