He walked to a small shed and tried the handle to the door. It was locked. He pulled a pair of metal picks out of his back pocket and knelt down. Iris glanced nervously around the alley. It was broad daylight, but the street was deserted. Everyone was at work except her. She hoisted her field bag onto her shoulder and fought back the urge to run. Within a few seconds the detective had picked the lock, and the door swung open.

He carefully shut it behind them and clicked on a flashlight. There was a giant hatch on the floor between them. It opened with a loud clank. Detective McDonnell followed Iris down a narrow ladder and into a tiny passageway. She pulled her own Magnum flashlight out of her bag and held on to it for dear life as the two of them headed down the dank tunnel.

After what seemed like miles, they reached a brick-lined, vaulted room that served as a junction point. Iris had been there before. She took the lead down the narrow passage that ended at the steep metal staircase. The sign above it read, “First Bank of Cleveland.” The first stair creaked loudly, and her heart skipped a beat. She froze and listened, before continuing to climb. At the top, Iris clicked off her flashlight and tried the handle to the access door. It wasn’t locked.

Daylight trickled down the stairs above them, giving just enough light to find their way across the lower lobby. The red carpet muffled their footsteps as they snuck across the floor toward the vaults in total silence. Iris dug her fingernails into the palm of her hand. This wasn’t happening, she told herself. It was just another bad dream. A police officer would not break into a bank. But that’s exactly what they seemed to be doing.

This was a terrible idea, but she had no choice. She was in danger. Someone knew about the keys. Someone had been watching her. The detective needed her help, and she needed his. There wasn’t a better plan, but she searched for one anyway. Maybe she could just try to leave town. The image of an abandoned brown suitcase was still hiding in a closet in her mind. Beatrice had tried to leave too.

The round doorway between the lower lobby and the vault corridor stood open. Iris couldn’t shake the feeling that they were walking into the open jaws of a beast.

All of the red velvet curtains of the private viewing rooms were pulled open except one. It was the shower curtain all over again as Iris stared at the red fabric from across the room. She stopped and strained her ears for the sound of a madman whispering her name. Detective McDonnell nudged her. They had to keep moving.

Through the round opening, they were greeted by total darkness. Iris felt her way across the marble corridor toward the vault that held over a thousand safe deposit boxes, each with its own little secret.

It felt wrong. Every other time Iris had visited the bank, the fluorescent lights had been buzzing, and Ramone had been wandering the halls. The detective clicked on his flashlight and examined the hundreds of tiny doors. He pulled out the keys he’d taken from her and began searching for Suzanne’s box.

The silence was closing in around her. She couldn’t shake the feeling of someone watching. Phantom voices whispered in her ears. She tried to tell herself if anyone was there, it would be Ramone. But he didn’t answer the ring of the call box. Maybe he was gone.

Detective McDonnell found Box 547. “So, how does this work?”

“Well,” Iris said, clearing her throat, “Suzanne’s key must go here, and the bank’s key goes in this larger hole.”

“And these are the bank keys?” He held up the ring of keys she’d found not far from where they stood. “So which one do we use?”

“Why don’t you just try them all?” There were only twelve keys, each with its own cryptic letter engraved on its face.

“The lock might break. The pins could be set to snap if the wrong key is forced in.”

She raised her eyebrows, and he raised his back.

“What, you think you’re the only one who does detective work? These markings don’t make sense. The keys are lettered, but the boxes are numbered.”

He handed the keys to Iris, and she looked through them. “U,” “I,” “N,” “D,” “E₁,” “O,” “S₁,” “P,” “E₂,” “R,” “A,” “M” the letters read around the ring. She’d wondered the same thing ever since she found them. There were tiny numbers on a few, but not all of them. Just on the letters that repeated, she realized.

“Oon Day-O Sper-Am.” Iris sounded out the letters aloud as she turned the keys over.

“Well, Deo is Latin for ‘God.’ ”

“Huh?” Iris scowled at the detective.

“It’s Latin. Twelve years of Catholic school,” he said with a shrug. “But who cares. I’m sure no one was thinking about God when they rigged this key system.”

“In God We Trust is the key!” she nearly shouted, and then clapped a hand over her mouth. In a lowered voice she explained. “That’s it! It was written in one of the files. ‘In God We Trust’ is written all over the dollar bill, isn’t it?”

Iris scrambled back to the vault corridor, where she had dropped her bag, and yanked out the file. “See! It says right here ‘In God We Trust is the key.’ Wait, there’s more.”

She pulled out another sheet from the file she’d found in the suitcase. “It’s a code or something.” Iris sat down on the vault floor with the notes and slowly translated.

“What the hell is all of that?” the detective asked, pointing his flashlight at the page of tick marks and bird tracks. “Where did you get those?”

“This stack of notes was in Beatrice’s personnel file. I thought it was weird, so I took them. And I found these”—Iris held up the other stack of paper—“in that suitcase up on the eleventh floor. Did you want to see it?”

His face was a stone. “First things first. You can read that?”

“It’s shorthand. I found this book, and I’ve been trying to make sense of it for weeks.” She dug out a pencil and wrote in the margins what she deciphered. “ ‘IN DEO SPERAMUS, one hundred at a time.’ ”

“In Deo Speramus means ‘In God We Trust,’ ” the detective confirmed softly.

“What’s the first box number?”

He walked deeper into the vault, searching both sides until he found the smallest number. “001,” he said, walking back to her. He paused and added, “The last number is 1299.”

“Okay, there are thirteen hundred boxes. If there was a key for each hundred of them, there should be thirteen keys, but there are only twelve.” Iris lay the keys on the ground and shined her light on them again. She arranged them until they read “I, N, D, E₁, O, S₁, P, E₂, R, A, M, U.” Iris trained her light back to where she’d found the keys hanging from a lock. The key still stuck there was labeled “S₂.” That was the thirteenth key. The man in the blue shirt must have forced it into the wrong lock. It was stuck.

“So, then, which one do we think goes to Box 547?”

“If I is 000, N is 100, then D, E₁, O . . .” She spun the key ring, counting. “S₁ must be 500, right?”

“Your guess is a hell of a lot better than mine.” The detective picked the keys out of her hand. “There’s only one way to find out.”

He stood up and slid the S1 key into the lock. He winced ever so slightly and gave it a gentle turn. The key rotated freely. Iris slid Suzanne’s key into the other hole, turned it, and the door swung open. Iris couldn’t help jumping up and down a little. They had done it.

“I guess they don’t let dummies into engineering school, huh?” He grinned.

Iris smiled back triumphantly. She had finally done something right. It was all going to work out now. Somehow.

Detective McDonnell reached in and pulled out a long, silver box. It looked like a miniature coffin to Iris. He carried it carefully to the counter outside the vault. The detective lifted the lid, and they both peered inside.