Body Double: A Rizzoli & Isles Novel

floor.”
    A moment passed in silence.
    Gary said, “We have GPR gear in the van. We used it two days ago, on a farm out in Machias.”
    “Bring it into the house,” said Rizzoli. “Let’s take a look at what’s under that dirt.”

TWENTY-TWO
    GPR, OR GROUND-PENETRATING RADAR, uses electromagnetic waves to probe beneath the ground’s surface. The SIR System-2 machine that the techs unloaded from the van had two antennae, one to send out a pulse of high frequency electromagnetic energy into the ground, the other to measure the echoing waves bounced back by subsurface features. A computer screen would display the data, showing the various strata as a series of horizontal layers. As the techs carried the equipment down the steps, Yates and Corso marked off one-meter intervals on the cellar floor to form a search grid.
    “With all this rain,” said Pete, unrolling electrical cable, “the soil’s going to be pretty damp.”
    “Does that make a difference?” asked Maura.
    “GPR response varies depending on the subsurface water content. You need to adjust the EM frequency to account for it.”
    “Two hundred megahertz?” asked Gary.
    “It’s where I’d start. You don’t want to go any higher, or we’ll get too much detail.” Pete connected cables to the backpack console and powered up the laptop. “That’s going to be something of a problem out here, especially with all these woods around us.”
    “What do the trees have to do with it?” Rizzoli asked.
    “This house is built on a wood lot. There’s probably a number of cavities under here, left over from decayed roots. That’s going to confuse the picture.”
    Gary said, “Help me get on this backpack.”
    “How’s that? You need to adjust the straps?”
    “No, they feel fine.” Gary took a breath and looked around the cellar. “I’ll start at that end.”
    As Gary moved the GPR across the earthen floor, the subsurface profile appeared on the laptop screen in undulating stripes. Maura’s medical training had made her familiar with ultrasounds and CT scans of the human body, but she had no idea how to interpret these ripples on the screen.
    “What are you seeing?” she asked Gary.
    “These dark areas here are positive radar echoes. Negative echoes show up as white. We’re looking for anything anomalous. A hyperbolic reflection, for example.”
    “What’s that?” said Rizzoli.
    “It’ll look like a bulge, pushing up these various layers. Caused by something buried underground, scattering the radar waves in all directions.” He stopped, studying the screen. “Okay, here, see this? We’ve got something about three meters deep that’s giving off a hyperbolic reflection.”
    “What do you think?” asked Yates.
    “Could be just a tree root. Let’s mark it and keep going.”
    Pete tapped a stake into the ground to mark the spot.
    Gary moved on, following the grid lines back and forth, as radar echoes rippled across the laptop screen. Every so often he’d stop, call out for another stake to be planted, marking another spot they would recheck on the second walk-through. He had turned and was coming back along the middle of the grid when he suddenly halted.
    “Now this is interesting,” he said.
    “What do you see?” asked Yates.
    “Hold on. Let me try this section again.” Gary backed up, moving the GPR across the section he had just probed. Inched forward again, his gaze fixed on the laptop. Again he stopped. “We’ve got a major anomaly here.”
    Yates moved in close. “Show me.”
    “It’s less than a meter’s depth. A big pocket right here. See it?” Gary pointed to the screen, where a bulge distorted the radar echoes. Staring down at the ground, he said: “There’s something right here. And it’s not very deep.” He looked at Yates. “What do you want to do?”
    “You got shovels in the van?”
    “Yeah, we’ve got one. Plus a couple of trowels.”
    Yates nodded. “Okay. Let’s bring them down here. And we’re going to need some more lights.”
    “There’s another flood lamp in the van. Plus more extension cords.”
    Corso started up the stairs. “I’ll get them.”
    “I’ll help,” said Maura, and she followed him up the steps to the kitchen.
    Outside, the heavy rain had lightened to a drizzle. They rooted through the CSU van, found the spade and extra lighting gear, which Corso carried into the house. Maura closed the van door and was about to follow him with the box of excavation hand tools