I’d already been back here for a while, and I knew that the longer I stayed, the more likely it would become that I would get caught. Reluctantly, I gave up the search and crept back over to the bookcase.

If Susan had chosen a random set of numbers to be her combination, then I had no hope of figuring it out. But most people don’t use random numbers. I had a few ideas for what the combination could be. First I tried the museum’s address, which I had just found written down in Susan’s office. It didn’t work. I tried the year the museum had opened, and the last four digits of the museum’s phone number. Frustratingly, the door remained locked. Whatever Susan had chosen as her combination, it wasn’t written down in her office.

As a last resort, I tried just knocking on the door. If Grace and Jacob were trapped back there, maybe they would hear my knock and know that someone was searching for them. After knocking a few times, I pressed my ear to the door and listened. It was completely silent.

I let out a deep breath. I had been so certain that I’d be able to get through this door, and if I couldn’t find a way inside, I really wasn’t sure what to do next. I decided to check Susan’s office one last time and was just about to walk back out from behind the bookcase when I heard a voice say, “Now, really.”

I stopped moving. Whoever was in the hallway couldn’t see me yet, but I must have been making a great deal of noise as I typed codes into the door’s keypad and tried to force the door open again and again. Not to mention the knocking.

“Yes, I heard you,” said the voice. “You can come out now.”

I could recognize the voice now. It was clearly Susan’s wheezing, nervous way of speaking. Reluctantly, I made my way out from behind the bookcase and turned to see her standing in the hallway with her arms crossed over her chest.

Right as I stepped out, I noticed that Susan had been watching the bookcase with her eyes narrowed and her expression stern. But as soon as she saw that it was me, her expression turned to one of complete shock.

I wasn’t sure what to make of the way Susan was looking at me. All I knew was that I desperately wanted to get behind that door.

“Oh, you’re here?” Susan asked me. I thought it was a strange way to phrase that question. Even more strange, however, was the way Susan was looking at me. She was staring at me like she was perhaps a bit frightened. I nearly questioned her about this, but instead I decided that getting behind that door had to be my first priority.

“I know,” I said. “I’m sorry, I shouldn’t be back here. But I really need you to open this door. I think the missing people from the photographs, Grace and Jacob, are trapped in whatever space is back there.”