I uncorked a vial of nitric acid solution, my hand steady as I drew a single drop into a glass pipette.

“If Leo used a standard formulation, the acid will turn the fiber a dull brown,” I explained.

“And if he didn’t?” Aries asked.

“If there is something else in the thread, the reaction will be different,” I said.

I let the drop of acid fall onto the gray wool.

For a second, nothing happened.

Then, the fiber began to hiss, a tiny wisp of pale green smoke rising from the ceramic dish.

The smell of bitter almonds and scorched sulfur hit my nostrils.

I took a step back, my eyes watering.

“Cyanide derivative,” I whispered, pointing to the dark, blistered stain on the wool. “It was bound to the metallic salts in the dye.”

Aries did not flinch, but his eyes narrowed to thin slits.

“Leo,” Killian said, his hand moving toward his holstered weapon. “The bastard poisoned the vat.”

“No,” I said quickly, shaking my head. “That doesn’t make sense.”

Aries looked at me, his gaze heavy and demanding. “Explain.”