The bones made the crew stop. The accompanying smell made them back clear off. It was Maggie’s understanding that the foreman called the sheriff and the sheriff—in the hopes of finding a simple explanation—called the property’s previous owner, only to discover that she had been dead for almost ten years. Her executor had just sold the land to the federal government after leaving the property vacant for almost a decade. He was, according to the sheriff, now en route, despite being three hundred miles away when he received the sheriff’s call and despite having no explanation for the newly discovered bones. In fact, it was the executor who suggested the federal government be notified. After all, they were now the owners of this mess.

As for Maggie and Agent Tully? It was a fluke that they were here at all.

They had flown into Omaha early that morning on an unrelated matter, an entirely different search. Their flight from D.C. had been a rough one. Maggie’s stomach still roiled just at the thought of the lightning and rain that greeted their aircraft. She hated flying and the roller-coaster ride had left her white-knuckled and nauseated. When they stopped for gas and discovered fresh homemade doughnuts inside the little shop, Maggie bought only a Diet Pepsi. Tully raised an eyebrow. She rarely passed on doughnuts. Thankfully his concern dissipated after his second glazed cruller.

For weeks they had been spending a lot of time together either in cramped offices back at Quantico or on the road. Somehow they managed to remain patient with each other’s habits and quirks. Maggie knew Tully was just as tired as she was of highway motels and rental cars, both of which smelled of someone else’s perfume or aftershave and fast food.

Their search had started about a month ago after discovering a woman’s body. She had been left in an alley next to a District warehouse that had been set on fire. But the victim, Gloria Dobson—a wife, a mother of three, a breast cancer survivor—had no connection to the warehouse fire. In fact, just days earlier, Dobson had traveled from Columbia, Missouri, to attend a sales conference in Baltimore. She never made it to the conference.

Virginia State Patrol recovered her vehicle at a rest area off the interstate. In the woods behind that rest area, Maggie and Tully found Dobson’s traveling companion, a young business colleague named Zach Lester. Maggie had seen her share of gruesome scenes in her ten years as a field agent, but the viciousness of this one surprised both her and Tully. Lester’s body had been left at the base of a tree. He had been decapitated, his body sliced open and his intestines strung up in the lower branches.

It wasn’t just the nature of the murders but also the fact that the killer had taken on both Dobson and Lester—two apparently strong, healthy, and intelligent business travelers—and succeeded. That’s what convinced Maggie and Tully that this killer had done this before. Their boss, Assistant Director Raymond Kunze, agreed and assigned them to the FBI’s Highway Serial Killings Initiative.

The initiative had been started several years earlier, creating a national database that collected, assessed, and made available details of murder victims found along the United States’ highways and interstates. Not a small task. There were currently more than five hundred victims logged into the system. The database allowed local law enforcement officers a way to check to see if bodies discovered in their jurisdictions could possibly be related to other murders in different states.

Maggie had easily bought into the project’s core belief that many of these murders were the work of serial killers who used the interstate systems. Tully jokingly called it a serial killer’s paradise. The rest areas and truck stops that provided safe havens for exhausted travelers also provided perfect targets for experienced killers. Though most were well lit, they were surrounded by woods or other isolated areas, and they provided a quick, easy escape route. In a matter of hours the killer could cross over into another jurisdiction undetected.

Bolstering the initiative, one killer had already been captured in 2007. Bruce Mendenhall, a long-haul truck driver, had been convicted of murdering a woman he picked up at a truck stop. He was suspected of killing five others from as many as four states.

The brutal murders of Gloria Dobson and Zach Lester led them to believe that they had stumbled across another highway killer. But their murders were only part of the reason Maggie and Tully had ended up in the Midwest. The killer had actually left Maggie a map. Just when they had finished solving the warehouse arsons in the District, Maggie discovered the map on the burned remnants of her kitchen counter. Her beautiful Tudor house, her sanctuary, had been set on fire. Her brother, Patrick, and her dogs had almost died inside.

But this highway killer had nothing to do with the fires. He had only taken advantage of them. The warehouse fires had been an opportunity for him to dump Gloria Dobson’s body in the alley. And the blaze that almost destroyed Maggie’s home was another opportunity. This one allowed him to invade her privacy. He had walked right into the ashes after everyone was gone and set the map on the granite countertop, anchoring it down with a rock from the ravine behind her backyard. The map was his invitation to a scavenger hunt.

The crude, hand-drawn diagram included wavy lines labeled “MissRiver” running parallel to more lines that looked like an interstate highway, complete with exits. Nothing else was marked other than north and south, east and west.

A young agent at the FBI’s crime lab, a data genius named Antonio Alonzo, had discovered the “MissRiver” was the Missouri River after he discounted all possibilities of it being the Mississippi. Then he insisted that the stretch of highway had to be Interstate 29. That narrowed Maggie and Tully’s search to seven hundred miles and thirty-two rest areas. Still a daunting amount of miles to cover.

Also on the killer’s map was a rest area, drawn out in geometric shapes precisely penned to indicate the buildings, picnic shelters, and a parking lot with slots for cars and trucks. A kidney-shaped road swirled around it, connecting it to the interstate exits. Squiggle shapes—what Agent Alonzo determined were woods—separated the rest area from the river. More squiggles—supposedly more woods—stretched on the other side of the river, fading out to a series of X’s, one after another, perhaps shorthand for more terrain.

That was Agent Alonzo’s theory. Maggie suspected that the X’s marked the spaces where he had dumped dead bodies.

Using aerial photos from truckers’ websites and Google Earth, Agent Alonzo had narrowed down the rest areas to three in Iowa, one in Kansas, and two in South Dakota. Maggie and Tully had been on the road for only a couple of hours when Agent Alonzo called. Human bones had been discovered the day before on a farmstead. The property backed to an interstate rest area. One of the rest areas on their list.

Now Maggie was anxious to see just how close the rest area was to this farmstead. Maybe this was just another detour on their wild goose chase. The skull and femurs could be an odd and unfortunate coincidence, depending on how old they were. She knew this was Indian territory once upon a time. The farm’s buildings were almost a century old. It was possible they could have been built over an Indian burial ground.

Still, she wanted to see for herself. She excused herself from the sheriff and his deputies, gave a knowing look to Tully, and left them. The long driveway had been blocked off by a single black-and-white sheriff’s SUV. One deputy sat bored in the driver’s seat. Maggie could hear the talk radio station. She nodded at him and noticed he shifted expectantly but she didn’t stop. She continued walking past a hedge of lilac bushes. Their flowers were only starting to open, but Maggie could already smell them.