But it was not blood they sought tonight. They were searching for something far more difficult to see, and for that, they required an alternate light source that was intense enough to reveal what was now invisible to the unaided eye.

Rizzoli knew that light was simply electromagnetic energy that moved in waves. Visible light, which the human eye can detect, had wavelengths between 400 and 700 nanometers. Shorter wavelengths, in the ultraviolet range, were not visible. But when UV light shines on a number of different natural and man-made substances, it sometimes excites electrons within those substances, releasing visible light in a process called fluorescence. UV light could reveal body fluids, bone fragments, hairs, and fibers. That’s why she had requested the Mini Crimescope. Under its UV lamp, a whole new array of evidence might become visible.

“We’re about ready here,” said Mick. “Now we need to get this room as dark as possible.” He looked at Korsak. “Can you start by turning off those hall lights, Detective Korsak?”

“Wait. What about goggles?” said Korsak. “That UV light’s gonna blast my eyes, right?”

“At the wavelengths I’m using, it won’t be all that harmful.”

“I’d like a pair, anyway.”

“They’re in that case. There’s goggles for everyone.”

Rizzoli said, “I’ll get the hall lights.” She walked out of the room and flipped the switches. When she returned, Korsak and Mick were still standing as far apart as possible, as though afraid of exchanging some communicable disease.

“So which areas are we focusing on?” said Mick.

“Let’s start at that end, where the victim was found,” said Rizzoli. “Move outward from there. The whole room.”

Mick glanced around. “You’ve got a beige area rug over there. It’s probably going to fluoresce. And that white couch is gonna light up under UV, too. I just want to warn you, it’ll be tough to spot anything against that background.” He glanced at Korsak, who was already wearing his goggles and now looked like some pathetic middle-aged loser trying to appear cool in wraparound sunglasses.