Around eleven on a Wednesday night, Don entered the Eppes house. He put his keys and jacket down and headed for the kitchen. Charlie was reclining on the couch, an afghan over his legs and a book in his hands.

"Hey, Charlie. Dad still up?"

"No." Charlie laid the book down. "He went to bed about an hour ago. He's got a client meeting in the morning."

Don walked past Charlie and into the kitchen. "Anything good on TV?" he asked as he opened the fridge and searched the shelves. It was too late in the evening to catch any part of the Dodger game worth watching but maybe there was an old movie on or something. Ever since his fight with Colby…who deserved every word of that threat of jail time, in Don's opinion…things had been strained at the office. Don needed to shut his brain off for an hour or ten.

"I don't know. I've been, um, I've been reading."

After opening a bottle of beer Don put some of the evening's leftovers in the microwave. "Anything someone without three college degrees could understand?" he called into the living room.

"Yeah, actually. It's this…." Charlie laughed in airy disbelief. "Dad was reading it, actually, for his, um, his book club. Swore up and down it would change my life, but not until the third book in the series. I'm near the end of book one right now."

The bell rang on the microwave and Don pulled the steaming meat and vegetables out, wrapping a towel around the edge of the plate. He grabbed a fork and sat down in the chair across from Charlie, who now had the book face open in his lap. "What, is he reading some kind of self-help series? How to Acquire Grandchildren in Seven Easy Steps?"

"No, it's, it's about this boy who finds out on his eleventh birthday that he's a wizard and he goes off to this place called Hogwarts and he's got this professor, right? And the professor absolutely loathes him and--"

Don nearly choked on his dinner. "You're reading Harry Potter?"

"You…you've read it?" Looking interested, Charlie sat up and leaned forward.

"Course I've read it." Leave it to Charlie to perennially forget that he was the one living in the bubble of academia, not everyone else. "Everyone has. I've read all the books in the series so far, actually. Megan was the one who got me into them. Said they were a great study in good and evil, with mass murders and mass fear in society. They're good." He washed some of the vegetables down with his beer, enjoying the rare opportunity to play the authority on anything analytical involving Charlie. "The books…it's like there's sort of a mystery, because you see what's going on but you know there's got to be a lot more behind the scenes. People aren't what they say they are and things that happen in the first, like, two or three books come back and--"

"Stop!" Charlie held up his hands. "No spoilers! I want to read for myself and see what happens."

A slow smile spread across Don's face. "How long do you think it'll take you to get to the end of book six?"

"I don't know. I guess it depends on how good the first five are."

Don couldn't stop grinning. Charlie, of all people, reading Harry Potter. He'd be done in two weeks, tops, if Don knew Charlie even half as well as he thought he did. "How did Dad talk you into reading that?" he asked. "You never read."

Indignant, Charlie replied, "I do so read! I read academic journals and the newspaper and…and I finally got around to reading The Math Gene. It was pretty good, too."

"Uh huh."

"It was!" Charlie was laughing now. "You have so little faith in me."

"When it comes to books that have more words than numbers, yeah, buddy, I do."

Charlie grabbed a pillow off the couch and threw it at Don, who almost knocked his plate over deflecting it. "Go away. I want to read."

Picking up his plate, Don stood. "You'll like the end of that book. There's this game of chess where--"

"Don, shut up!"

Don finished his dinner at the table, rinsed his dish, and put it in the dishwasher. His beer bottle went into the recycling bin. He briefly considered staying for the night, but he decided he'd rather sleep in his own bed.

Charlie was still deep into Harry's adventures when Don closed the door and climbed into his SUV, heading for home.

The next few days in the FBI office were a blur of files and frustration, interrupted briefly when Charlie came in to work on some of his newest equations. When Charlie pulled out his laptop on Thursday Don caught the glint of green foil lettering and the number 3 in a box printed on the spine of a book in Charlie's bag. Don had to put his hand over his mouth to hide his smile. Four days and Charlie was already on the third book. With everything else going on, Charlie had to be completely addicted, reading in every spare moment, in order to progress that fast.

Secretly Don wanted to begrudge Charlie the time he took to read for pleasure, but he couldn't. The FBI wasn't Charlie's world and it shouldn't impede on Charlie's time. Charlie did so much for them; he deserved some time to sit with a book and forget about all the crazy shit happening in the office. He deserved sleep and hot meals and showers at regular intervals, all of which Don was more than desperate for at this point.

"Don?"

"Don!"

"What?" Don looked up from the contents of Charlie's bag. "Sorry. Yeah, what about that…the metric…algorithm…thing you were talking about, Charlie?"

Charlie got about a sentence out before Don found himself spacing again. Megan slid her coffee across the table and tapped his arm. Looking into the cup made Don feel ill. He held his hand in front of the cup and shook his head. He knew law enforcement was his calling but there were days like today when he thought he should have become an accountant. Or maybe an actor. Caffeine wasn't going to fix the uneasiness he couldn't shake about Colby, or the criminals he had to pursue.

Charlie had a class to teach that afternoon but Don had promised to go by the house for dinner. It was just as well. He was pretty sure his fridge didn't contain much more than beer, spoiled milk, and wilted lettuce.

When he entered the house he heard voices in the kitchen. Alan was making what Don recognized by smell as shrimp scampi and Charlie was slicing tomatoes and talking excitedly.

"The probability of all this happening and Lupin never knowing a thing about what Peter did to Sirius and how he betrayed the Potters…it's infinitesimal. That Sirius spent twelve years in Azkaban for not doing anything and no one discovering the truth is an anomaly. It could have only happened under very exact circumstances. And Snape! How could he not see it?"

"Because he didn't want to believe the truth," replied Alan. "It's like what Doyle wrote in Sherlock Holmes: Once you have eliminated the impossible, whatever remains, however improbable…"

"…must be the truth," chimed Don. "Yeah, I remember that."

"That is true and…fascinating," said Charlie, gesturing with the knife so emphatically that Don flinched.

"Hey, watch where you're pointing that," Don said, holding his hands up in a defensive position.

Charlie looked at the knife for a moment as though he'd forgotten what it was for. "Oh. Sorry. But you know, that thing you said, I think it applies to so much of what's in these books. Like Ginny Weasley in book two. No one believed she did all those things but…it was improbable, but not impossible." Charlie finished slicing the tomato and mixed it into the salad greens. "I'm thinking I might run some statistical analyses of these characters. You know, chance of mortality, happiness, risk factors for turning to Voldemort… Could be interesting, and maybe…maybe it'll tie in with my cognitive emergence work. The math of literature."

Don reached for the salad bowl and took it into the dining room. "Wait until you finish the sixth book," he called back into the kitchen. "That'll affect your data sets or whatever you call them."

"I could start doing this now," Charlie said when Don came back to get plates and silverware. "I've got enough data to start. I was even thinking I could use math to predict some of the major events."

As he set the table and lit a white candle in the center, Don smiled and said, "You do that. Millions of fans haven't been right yet."

Two weeks passed before Don was able to get to the house again. Things were more or less back to normal with Colby and Don, though it had been difficult, had buried the Dwayne Carter hatchet. After a twelve-hour day, Don came to the house and found Charlie in the garage facing a set of blackboards and muttering to himself.

"I should have seen that coming. He cared too much." Charlie erased something at the top of a long column of numbers on one of the boards. Approaching the board, Don could see the columns were labeled: Harry, Ron, Hermione, Lupin, Snape, D. Malfoy, Sirius, Dumbledore, Arthur, Molly, Ginny. Six rows across completed the grid, and they were labeled as well: SS, CoS, PoA, GoF, OotP, HBP. Don had a flashback to an undergraduate class he'd taken in linear algebra and realized the labels, laid out in a matrix of staggering proportions, were abbreviations for the six Harry Potter books.

"You're really doing this Harry Potter math thing?" asked Don, incredulous.

"J.K. Rowling ishorrible at math, did you notice? She can't even decide how old Charlie Weasley is and there's one student, Marcus Flint, who she totally forgot about and she's got him as a seventh-year twice. Honestly, I don't understand how this woman can make millions of dollars and not be able to add and subtract," Charlie replied as his chalk clacked across the board.

Don almost replied, "Yes, if you'd spend three minutes Googling Harry Potter you'd have saved yourself a lot of time and frustration over J.K. Rowling's math." There was no point in doing that, though. Aloud, he asked, "So…what's your ultimate goal here, Charlie?"

Shrugging, Charlie said, "Publish a paper. Put this towards my cognitive emergence work. Impress the hell out of people who think I don't read."

Don snorted. "Oh, yeah, you'll be beating Dad at Scrabble any day now." He ducked as a piece of chalk came flying at his head. "You know, there's still one book to go," he continued.

"I know. I'm thinking that with this statistical analysis, I can accurately predict who will die in the last book. Do you remember that workup I did with the risk factors when you had those three suspects with the dirty bomb and we talked about the prisoner's dilemma?"

"Yeah. You talked about who had the most to lose in terms of family and all that. I remember."

"Well, this works the same way. I can take variables like family, academic success, economic status, status during the first war, family history of wizarding, and links to either the Death Eaters, the Ministry of Magic, or the Order of the Phoenix and use them to create a matrix that will predict who has the highest chance of mortality. If I adjust the weights of the variables for different emotions, those same variables should also show me who some of the couples will turn out to be."

"What, because it's not blatantly obvious that Ron and Hermione will end up married? I don't need math to tell me that. Ron acts around Hermione just like you did around Val Eng."

Charlie's jaw dropped. "I…I don't know what you're talking about." He turned away so Don couldn't see his face.

"Yeah, all right, buddy, you go ahead and believe that."

Holding up his left hand, Charlie replied, "Not listening." He continued to write.

Staring at the chalkboard, Don saw a few symbols and words that looked vaguely familiar. It had been a while since he'd taken calculus but he recognized an iterated integral on the far side of the board. There was a box drawn around it, so it had to be important, but… Don struggled for a name. Limits of integration. That was it. There were no limits of integration and he wondered what the variables represented. Integrals were supposed to find…volume? Area? Something like that. He felt a twinge at his temple, the beginning of a headache, and pressed against it with his fingertips. "So who do you think is going to die?" he asked after a moment.

Charlie's chalk never stopped tapping as he replied, "Snape. And it's looking like Draco Malfoy, and at least one of the Weasleys. Lupin and Pettigrew each have a greatly increased chance of dying because of what happened to James and Sirius. I'm not done with this, though."

As Charlie wrote, Don looked over the boards again and recognized a sine curve. What the hell did trigonometry have to do with any of this? The pain continued to pulse in his temple. "Don't you have papers to grade or consulting work to do?"

Looking over his left shoulder, Charlie said, "Don, sometimes I have to work on what's in my head. And this is what's in my head."

Don tried to smile, but the words echoed in his head and he shivered at the remembrance of the last time Charlie had said them. For a moment he wondered if he should say something, try to dissuade Charlie from getting too deep into this Harry Potter math. The last book was probably going to be out in a year and Charlie would have all his answers anyway, but that didn't stop Don from remembering what Charlie could be like when he had to work on what was in his head. Don got up to leave but he stopped at the doorway and turned around.

"Charlie?"

"Yeah?"

"Is everything okay?"

Charlie paused, holding the chalk in mid-air, and looked perplexed. "Yes. Why wouldn't it be?"

Words like "Mom" and "P vs. NP" and "three months" formed a tangle at the back of Don's tongue. "Um…nothing. Don't…don't worry about it. Look, I'm going to head to my apartment. I'll see you tomorrow?"

"Sure," Charlie said, nodding absently and turning back to the chalkboard. "Yeah."

The next time they had some down time together, Charlie invited Don out to the garage. Charlie's boards were filled with equations and scribblings of various colors. The iterated integral had been worked and reworked, with different limits of integration. The variables, Don saw now, represented characters: For each calculation, the names of the specific characters were written below the integral and the limits were different. Of course, he had no idea what the limits of integration meant, but he didn't want to know badly enough to ask.

"You're still working on this Harry Potter thing? By the time you finish the last book is going to be out," Don teased.

"You know, I went back and reread the end of book five, everything from Sirius's death onward, and I realized I was missing two huge variables." Charlie, nonplussed by Don's remark, walked over to one of the boards and picked up his chalk holder and walked over to the sine curve Don had seen last time. There were faded chalk lines underneath it, indicating that Charlie had redrawn it at least twice. Taller, shorter, wider, narrower…what was the word…? Amplitude.

Don sat on the worn couch, propping his right ankle on his left knee. "And what are those?"

"Love and power. See, one is about how much you have, and the other is about how much you want. There's the question of the ratio of how much you love, and how much others love you, to your chances of survival For a while, I thought the pattern there might be sinusoidal—you know, up and down, depending on whether you're around those who love you or those who hate you—and that they would relate to each other enough so that it would all be predictable, but that doesn't seem to be the case. I even tried a dampening effect so that the whole thing would die down to zero as time goes to infinity, because eventually, when people die, there's no love or hate for them, right? But it doesn't quite work that way. Even though Rowling clearly wants us to think that the desire for and acquisition of love is a good thing and the desire for and acquisition of power is bad, what happens to the characters it…it doesn't always add up. Voldemort has no love, and the logical conclusion would be that conversely, Harry has no power. But that's not the case. Voldemort doesn't desire love and Harry desires power."

"Well, Harry wouldn't be able to defend himself if he had no power," Don reasoned. "I mean, when I'm out in the field I get a gun. And…wait a minute." Don turned Charlie's words over in his mind. Helping Charlie was actually sort of fun when he could understand what Charlie was saying. "No, no, no, you said that Harry desires power. That's not true."

"Sure it is." Charlie folded his arms across his chest. "He wants the power to defeat Voldemort. Harry's going to have to kill him, and that requires power."

The thoughts were falling into place in Don's head, and he stood and started pacing. He could never think clearly when he was sitting. "You're being too literal."

"Don, math is literal."

"That's not what I meant." Don walked over to Charlie's board and rummaged around for a piece of chalk. "There's another factor to your equation."

Charlie turned and reached to get chalk off a ledge under a second board. He presented it to Don. "It's not a factor, it's--"

Don took the chalk from Charlie and wrote NORMALCY under one of Charlie's tables. "You're wrong about Harry wanting power. He doesn't want power. He wants a normal life. He wants…" Don grinned. "He wants what Dad wants for us: A wife and a white picket fence and 2.5 children and a cocker spaniel. He wants to not see death all the time or be in danger or have his picture in the paper."

"Dad…" Charlie shook his head. "You know, I hadn't thought of it that way." He made a tiny note to himself at the side of the board, muttering under his breath. "The normal distribution…the bell curve…transcendental functions…that could be it, after all…"

"You know what I don't get?" said Don, stepping back from the boards and scanning Charlie's work.

"A lot of things that involve math?"

"Oh, please." Don gestured to the boards. "You're standing here completely stumped by a woman who by your own admission can't add or subtract."

Indignant, Charlie snapped, "I am not completely stumped! I have," he said, pointing, "boards full of working equations. I have an algorithm that I believe will accurately predict the deaths that will occur in book seven. If I'm correct this could change the way the math and literature worlds interact. It could…it could change the face of liberal arts education."

"Since when have you cared about liberal arts education?"

Charlie shrugged. "Since a journal aimed at mathematicians in the liberal arts setting might be willing to publish my observations and Dad mentioned that we're going to need a new furnace in the not too distant future."

There was no arguing with Charlie's logic. "Yeah, well, hope you finish before the weather gets cold. I need a beer. You want one?"

"No thanks." Charlie's shoes squeaked on the floor as he turned back to the boards.

On a Saturday afternoon a few weeks later Charlie invited Don's team, Larry, and Amita over to see his work.

"I know you guys aren't the normal audience for the unveiling of a math theorem," said Charlie, pulling chairs into place around his chalkboards, "but I wanted someone who's…familiar with the canon." He pushed his hair out of his eyes. Looking up and smiling, he said, "Hey, Colby." They shook hands and Charlie pulled Colby to him for a pat on the back. "Have you read the books?"

"Oh, yeah," Colby replied, dropping Charlie's hand. "Two little nephews. Every time I take a trip to Idaho they want me to read to them. 'Do Professor Snape's voice, Uncle Colby.' They love the books so I read to them and, y'know, they really weren't too bad."

"Great, then, you've…you've read them. Um, why don't you have a seat? Do you want something to drink? Here, sit down." Charlie cleared a space for Colby on the couch.

"I'll take a beer as long as you're getting Colby that drink," said Don in a tone that indicated he hadn't missed Charlie's bid at hospitality.

Megan stared in awe at the boards, marveling at Charlie's work. "How did you come up with all this?"

Charlie's face lit up. He opened his mouth and Don could see an hour-long lecture coming, a lecture that involved a lot of words no one could understand and a lot of analogies that would just waste time. Another headache was starting in his temple, tightening his jaw and burning into his upper back. He was in no way prepared to listen to Charlie's lecture without a beer in his hand.

Turning to Megan, Don said, "Magic."

--

end