“What we couldn’t understand,” Polina went on, “was why we didn’t find a timer or remote receiver. I did some research. You don’t need a separate source of ignition if you combine red sodium and copper sulfate.”

Arkady looked at the pots at his feet again. RS: red sodium, marine-paint red, a deep carmine with an ocher tinge. CS: copper sulfate, a vile stewpot green with a sniff of the devil. He put his matches away. “You don’t need a fuse?”

Polina set the wet board down on the Zil’s front seat and brought out another on which the green paint was dry. Over the board she taped brown paper. “Red sodium and copper sulfate are relatively harmless individually. Together, however, they react chemically and generate enough heat to spontaneously ignite.”

“Spontaneously?”

“But not immediately and not necessarily. That’s the interesting part. It’s a classic binary weapon: two halves of an explosive charge separated by a membrane. I’m testing different barriers such as cheesecloth, muslin and paper for time and effectiveness. I’ve already put painted boards in six cars.”

Polina took the brush from a can marked RS4 and started painting the paper in broad strokes of red sodium. Arkady noticed that she started with a W, like a house painter. “If they did ignite immediately, you’d know by now,” he said.

“Yes.”

“Polina, don’t we have militia technicians with bunkers and body armor and very long brushes to do this sort of thing?”

“I’m faster and better.”

Polina was quick. She kept red drips from falling into green cans and in less than a minute covered the papered board so that it had a completely scarlet surface.

Arkady said, “So when the wet red sodium soaks through the paper and makes contact with the copper sulfate, they heat up and ignite?”

“That’s the idea, put very simply.” Polina took a notepad and pen from her raincoat and jotted the paint numbers and the time down to the second. With finished board and brush in hand, she started to stroll down the line of wrecks.

Arkady walked with her. “I can’t help thinking you’d be better off skipping through a park or sharing an ice cream sundae with someone.”

The cars on the dock were crushed, rusted and stripped. A Volga was so twisted that its axle aimed at the sky. A blunt-nosed Niva wore its steering wheel through the front seat. They passed a Lada with its engine block resting ominously in the rear. Around the dock were darkened factories and military depots. Out on the river, the last hydrofoil of the evening slid by like a snake of lights.

Polina laid the red board by the brake pedal of a four-door Moskvitch and painted a 7 on the left front door. When she saw Arkady begin to approach the other six cars on the end of the dock, she said, “You’d better wait.”