Monday, eight forty-five. New Yorkers were distracting themselves from worrying about the holidays by worrying about the Millennium Bug. I had prepared by having so many leftovers from Thanksgiving that I could live on them until February. My name is Tuesday. I'm a mathematician.
I picked up my messages from Sgt. Abruzzi on the way in and arrived at my office to find my partner, George Frankly, staring intently at a slot car track he had set up on his desk. And mine.
"Are we starting a Mathnet division of Formula 1, George?" I asked, leaning over his shoulder.
George turned around, startled. "Pat! I was just thinking about calculus. See, as the cars go around the track, their position is constantly changing."
"And if we measure how fast that position is changing, that's what mathematicians call the derivative of the cars' position."
"And which is better known as their velocity. And if we measure how fast the velocity is changing, we get the derivative of the velocity..."
"Also known as their acceleration. So are you expecting us to solve a crime at the slot car races?"
"In this job, Pat? You never know!"
The door opened and our captain, Joe Greco, came in, looking puzzled. “You guys know anyone planning on a swim this weekend?”
George looked at him, taken aback. "It's the middle of December, chief. That would be extremely dangerous! Why do you ask?"
"Because a Coast Guard patrol boat picked up someone in Long Island Sound this morning, and the one thing she said before collapsing was 'Mathnet'. She's down at Bellevue now. Go check it out."
"We're on it, chief." I nodded at George. "Let's roll, pard." We stood, checked our calculators, and left.
Our friend Benny Pill drove us uptown to Bellevue Hospital, where we were met by Dr. Jordan Santiago. We introduced ourselves and she took us to the room where our mysterious patient was being treated. "Does she look familiar to either of you?" she asked.
George and I shook our heads at each other. The woman in the bed was in her mid-to-late twenties, with wavy black hair, possibly South Asian. "We've never seen her before," I said. "Will she be all right?"
Dr. Santiago nodded cautiously. "We think so. She was very chilled, but she seems to be in good health generally, and there's no sign of brain damage. She probably won't be conscious until at least tomorrow, though."
"Could we see her personal effects?" asked George.
"The only thing she had other than the clothes she was wearing was this notebook, but it's in some sort of code." She handed us a small black notebook, which was still cold and slightly damp. I opened it, to find that it was full of numbers. "If you can use that to find out who she is, that would be very helpful."
We made copies of the notebook pages and took them back to the office. As George stowed his slot cars, I started looking at the first page of notes. I went to the board and wrote up the first few lines.
"Well, that certainly looks like a code for the alphabet, Pat." George said, looking up at the code as he put the slot cars down. "The numbers are in small groups, they're all between 1 and 26, and there's even punctuation."
16 * 11 22 21'1 * 1 15 16 21 18 * 1 15 12 * 23 19 8 21 * 16 26 * 1 22 * 26 1 12 8 19 * 1 15 12 * 26 18 16 11 26.
"That's what I thought, but it's not simply mapping 1 to A, 2 to B, and so on, like some of the other codes we've dealt with. Look." I wrote the corresponding letter under each number: P KVU'A AOPUR AOL WSHU PZ AV ZALHS AOL ZRPKZ. "And what do you think that first line means?"
"One equals two to the third power? It might mean that whoever wrote this is bad at math! Heh-heh-heh. Two to the third power is eight."
I gave George a look. "Let's assume that whoever wrote this notebook, probably our mystery swimmer, is competent at math. What if that's the key to reading the message?"
"So when she writes that one is eight, she means to read the number eight as if it were the number one, which is the letter A! So to read the message, we subtract seven from each number before converting it into a letter." George picked up a piece of chalk and wrote the new numbers underneath my letters:
9 * 4 15 14'-6 * -6 8 9 14 11 * -6 8 5 * 16 12 1 14 * 9 19 * -6 15 * 19 -6 5 1 12 * -6 8 5 * 19 11 9 4 19.
"Let's add 26 to those negative numbers to bring them back into the range of letters, George." I changed the -6s to 20s, then wrote letters underneath:
I DON'T THINK THE PLAN IS TO STEAL THE SKIDS.
"'I don't think the plan is to steal the skids'," George read. "What are the skids? And why would she write that? If she's part of the plan, shouldn't she know what it is? And if she's not part of the plan, why is she writing about it?"
"Maybe because she's trying to stop it," I said, realization dawning gradually. "George, what if she didn't say 'Mathnet' to the Coast Guard because she was looking for us? What if she said 'Mathnet'..."
"Because she is Mathnet!" George finished my sentence with me. "But if she's Mathnet, which Mathnet department does she work for? And where's her partner?"
"Right here," said a voice from the door. The woman standing there was instantly familiar, even though we'd never met. I'd seen her picture on records from George's old cases, and even though she was wearing a darker suit and a more severe haircut, the cheekbones were unmistakable. "Hi, George," said Kate Monday. "How's Martha?"