Sherlock and John had been traveling for less than an hour when grey ash descended from above like the aftermath of a volcano eruption. They had rolled the windows down because of the stifling heat, but the ash now made such ventilation messy and potentially dangerous.

"I don't know where we are," John said, trying not to sound desperate. They had decided to drive toward the city, to be closer to the airport when the crisis was finally averted. Lack of light and now, thanks to the ash, reduced visibility destroyed their sense of direction. John just followed the yellow line-which was rapidly disappearing beneath the build-up- and prayed that it would lead them somewhere safe.

Others were on the road too, their headlights cutting through the dusty torrents. Many more were literally off the road, due to erratic driving and traction problems in the ash accumulation. Injured, confused people huddled in these stranded vehicles and watched passing traffic, eyes and lips pleading for rescue. Each time John's foot applied pressure to the brake, Sherlock warned, "Don't."

John would protest. "I'm a doctor, God damn it! I can't leave wounded people-"

"You can and you will. Unless you want us to become just as bad off as they are."

He knew Sherlock was right, and hated it.

They had been driving for a few hours when a sharp glimmer in the shadows to their right caught John's eye. He slowed down and pulled over, but left the motor running.

"I see it," Sherlock said before he could speak. "It's a grow-op. I'm not surprised it would have an independent power source."

"Grow-op? How can you tell?"

"Obvious. Look closely- those are high-intensity lights, around 1000 watts if I'm not mistaken, and I rarely am. The building itself must be a barn, as a residence would have a proper driveway. In this remote location, it can't be anything but an illegal marijuana growing operation."

"Then let's move on," John said.

"What? Why?"

"Because if anyone's in there, they're probably armed, and got lots of firepower to spare. People in that type of business would kill a dozen men to protect a handful of plants."

"All the more reason to infiltrate." Sherlock reached into the back seat for a discarded T-shirt and wrapped it around his nose and mouth to avoid inhaling ashes. "I have a good idea of what lies ahead, John, and we'll need to meet it with guns."

Before John could stop him, he was out of the car and off like a greyhound, heading for probable disaster.

That meant John had to follow, and quickly.