Thanks to Skullgal94, AirRaider23, and SimonCatGirl for reviewing!
Once they arrived back at Basil's flat, Dawson quickly patched Veronica up, her stab wound required a few stitches, the first she'd ever had in her life. After she had been patched up, Basil had gotten to work on studying the list with his magnifying glass, as Dawson and Veronica watched.
"Offhand, I can deduce very little," Basil said. "Only that the words are written with a broad pointed quill pen which has spattered, twice. That the paper is of…" He tossed it in his hand, testing its weight. "Native Mongolian manufacture, no watermark. And has…" He put it to his lips and smacked it several times. "Been gummed, if I'm not very much in error…" He sniffed the paper but then held it out at arm's length in disgust. "By a bat who has been drinking Rodent's Delight! A cheap brandy sold only in the seediest pubs."
"Hmm. Amazing," Dawson said.
"Oh, not really, Doctor," Basil said, as he rummaged his desk. "We still don't know where it came from." He pulled out his microscope, as he said, "Perhaps a close inspection will tell us something." Focusing on the letter through his microscope, he said, "Hmm-hmm. Hmm. Coal dust. Clearly of the type used in sewer lamps."
Dawson tried to look through the microscope, but Basil had taken the letter and was holding it over a small flame, letting it catch fire.
"Uh, but, Basil, I-I," Dawson began.
"Shh! Don't speak," Basil said.
Basil let the ashen remains of the paper fall into a small bowl and patted it down with a small wooden masher. He poured the contents into a glass jar of yellow chemical, which turned blue. Dawson stared at the liquid with his bifocals, but Basil had returned with a vial of a red chemical.
"Excuse me, Dawson…" Basil said, as he held the red chemical over the jar. "Steady hand."
Basil let a single drop fall and a small puff of smoke came out, as the chemical turned violet. He set the jar below a glass spout and reached to the other side of the chemistry set to turn on a small flame.
The green chemical inside bubbled up and slowly made its way through the tubes, as Basil encouraged it softly, "Yes, yes. Good, good. Come along, come along, come along, come along. Come along, come along, come along, come along…Ha-ha…Yes, yes, good, good. No, bad. Good, good, oh, no. Come along, come on. Yes, come on."
The three mice were now watching intently as a single green droplet was hanging above the violet chemical, even as Basil said, "Yes…Yes…" The drop fell and the chemical turned red. "Aha!" He said, putting his arm around Dawson. "We've done it, old fellow! This reaction could only have been triggered by the paper's extreme saturation with distillation of sodium chloride."
Basil moved away from the table, as Dawson and Veronica continued to study the now-clear chemical.
"Salt water?" Dawson said. "Great Scott."
Basil rummaged through his maps, as he said, "It proves beyond a doubt, this list came from the riverfront area."
He used his darts to pin a map of the riverfront to the wall.
"Ah, now, steady on there, Basil," Dawson said.
"No, no," Basil said. "Elementary, my dear Dawson. We merely look for a seedy pub at the only spot," here, Basil marked said spot with another dart, "where the sewer connects to the waterfront."
"Well, the only pub I would know where the sewer connects to the waterfront would be The Rat Trap," Veronica said.