The phone call that summoned us to D.C. came on a Friday evening in April. I was busy playing Frisbee with some pizza dough and Lauren was slicing garlic so thin it was translucent. Her hands were less sticky than mine were so she answered the phone.

A moment later, with real surprise in her tone, she said, "Hi, A. J. No, no, no.

You're not interrupting anything. Really. We're just throwing some dinner together… Yes, in our new kitchen, it's wonderful. It's good to hear from you… We're doing fine, thanks. You?"

I smiled. The only A. J. I knew was A. J. Simes, a retired FBI psychologist.

The previous year she had been instrumental in helping me identify and track down someone who was eager to kill me. Before the adventure was over she had saved my life. Lauren and I had only heard from her once since she had left Colorado and returned to her home in Virginia.

"You still in touch with Milt Custer, A. J.?" Lauren asked. Milt was also retired FBI, and had been A. J.'s colleague the previous fall.

A. J.'s response to the Milt Custer inquiry took a while. Milt, a Chicago widower, had been sweet on A. J. during their sojourn together in Colorado. I fondly recalled his awkward flirting. But Lauren's next words yanked me back to the present.

"You want our help with something?… Both of us?… Of course I'll listen.

Should Alan get on an extension? Good, yes… Hold on." Lauren covered the mouthpiece and said, "It's A. J. Simes. She wants our help with something. Why don't you get on the cordless and listen in to what she has to say?"

I grabbed the other phone from the front hallway and A. J. and I greeted each other. Immediately after the pleasantries she asked, "Have either of you ever heard of a man named Edmond Locard?" I said no. Lauren said she thought the name was familiar.

"Well, have you ever heard of an organization called Locard? It is, of course, named after Edmond Locard. He, by the way, was a nineteenth-century French police detective." We both said no, though Lauren had begun nodding her head as though she was remembering something about him.

A. J. sighed.

"Does the name Vidocq ring any bells? An organization called the Vidocq Society?"

"Yes," I replied.

"I've read something about them. It'sum a volunteer organization of law enforcement officers and-what?-forensic specialists and prosecutors who try to assist local police in solving old crimes. Murders and kidnappings mostly.

They've been quite successful, haven't they?"

"That's right, they have. Very good, Alan. Well, Locard is a group similar to the Vidocq Society and has similar goals, though a slightly, mmm, shall we say, different philosophy and approach. I am one of the founding members. We are not as well known as Vidocq, which is mostly by design. Our members are not as prominent. That, too, is partly by design. But as an organization we are very effective. The reason I'm calling is that we in Locard have just made a decision to consider involving ourselves with a case that involves a crime that occurred in Colorado over ten years back but that also has some intriguing contemporary Colorado connections. I suggested to our screening committee that I thought you could both be of some help in our efforts. You, Lauren, could advise us on the lay of the local prosecutorial landscape. And you, Alan, could help me with some aspects of the case that might involve your clinical skills.

The screening committee has already looked-discreetly, I assure you-into your backgrounds and authorized me to invite you both to consider assisting us on the case.

Should the case develop as we anticipate it will, you would each bring an important local perspective to our investigation." A. J. told us little more that evening. She did explain that our participation was purely voluntary, and that we would not be remunerated for our time or for our expenses except for extraordinary travel costs, which would need to be approved in advance by the director of Locard.

We looked at each other and shrugged. Lauren told her that we would be happy to consider her request. A. J. explained that we would need to come to Washington, D.C." at least once and possibly twice or more but that the Colorado family that was imploring Locard to investigate the crime had agreed to provide transportation for the initial visit.

"When would this be?" Lauren asked.

"The first meeting is a week from tomorrow. You would need to be at Jefferson County Airport at six o'clock in the morning. That's close to your home, right?

I'm told that it is."

"Yes, it's close enough."

"There will be a plane waiting for you there at a facility called…" She hesitated and I heard papers ruffle. "… Executive Air. The family name is Franklin. You should be back in Colorado the same day if you're lucky. Midday Sunday at the latest. If you're required to stay over, someone will make sleeping arrangements."

"And you'll be there, A. J.? At the meeting?" I asked.

"Yes, definitely. And one last thing."

We waited.

"Please don't tell anyone we've talked. Discretion is important. Essential.

Agreed?"

"Yes."

"She doesn't want us to tell Sam," I said, a few moments after we hung up the phone. Sam Purdy was a Boulder police detective and a good friend. A. J. had become acquainted with him the previous autumn, too.

"I got that impression, too," Lauren agreed.

"Any idea why?" I shook my head.

"Secrecy is its own reason. Can you finish making the pizza? I want to check some of this out on the Internet."

I sat down at the kitchen table fifteen minutes later.

"There isn't much about Locard as a group. A little about Edmond Locard as an individual. But the Vidocq Society has its own Web page. Lot of heavy hitters are members. You know, CNBC types-the kind of people who had endless opinions about Monica Lewinsky. Some people who testified in the O. J. trial. Vidocq has a fancy meeting room in a town house in Philadelphia. There's some blurb on their Web page about 'cuisine and crime."

Apparently, they have fancy lunches while they sit around and discuss old crimes. The Web page makes it sound like some kind of club. A regular crime-fighters' Rotary."

Though Lauren was drinking water, she handed me a glass of red wine.

"While you were on the computer I remembered where I'd heard his name before.

Locard. He's the man responsible for what detectives and crime-scene specialists call Locard's Exchange Principle. Its the foundation for the science behind trace evidence.

Locard's the one who theorized that when any two objects came in contact or stay in close proximity for an extended period, something, some material, either visible or microscopic, will always be exchanged between the two objects."

I smiled. "That's about all I learned on the Net, too. That and that Locard worked in Lyons. Can you believe we agreed to do this?"

"Yeah, I can. I think it sounds fascinating. I'm more surprised that we were asked. Let's face it, Alan, our national reputation as crime fighters is, shall we say… nonexistent. I suspect that A. J. has an agenda that we don't know about."

"Do you think it will take up much of our time?"

She shrugged.

"I know a couple of people who have done this sort of thing before. My impression is that its more of a consultation thing. I don't think it will be too bad. Anyway, we owe A. J. big-time."

"Yes. We do owe A. J. big-time." I lifted the pizza to my mouth.

"Gosh we make good pizza, don't we?"

We were in.

Our flight from Jefferson County Airport in Colorado to Washington National was on a private jet that had room to seat ten or so, depending on how many people squeezed onto the leather sofa in the center of the plane. On this nonstop, though, Lauren and I had been the only passengers. The whole private-jet, flight-attendant-acting-like-a-butler thing had led us to conclude chat we would be greeted on the tarmac at the airport by a shiny black limo with a liveried driver, or at the very least a Town Car with a chauffeur. Instead, as we descended the stairs from the Gulfstream and collected our bags from our always solicitous flight attendant, Ms. Anderson, we stood alone on the macadam watching the approach of a bright yellow fuel truck. After a minute or so one of the pilots followed us off the plane and suggested we might want to retreat to the waiting area that was inside the office of the company that was going to service the plane.