“I think all the lady wants to do,” said young Macgowan, “is give you a jab, Queen. She doesn’t think thinking is a substitute for footwork.”
“Each has its place,” Ellery said amiably ― “sit down, Laurel, won’t you? Each has its place, and thinking’s place can be very important. I’m not altogether ignorant of what’s been going on, seated though I’ve remained. Let’s see if I can’t― er― think this out for you...” He closed his eyes. “I would say,” he said after a moment, “that you two have been tracking down the arsenic with which Priam’s tuna was poisoned.” He opened his eyes. “Is that right so far?”
“That’s right,” cried Macgowan.
Laurel glared. “How did you know?”
Ellery tapped his forehead. “Never sell cerebration short. Now! What exactly have you accomplished? I look into my mental ball and I see... you and Mac... discovering a... can of... a can of rat poison in the Priam cellar.” They were open-mouthed. “Yes. Rat poison. And you found that this particular rat poison contains arsenic... arsenic, the poison which was also found in Priam’s salad. How’m I doin’?”
Laurel said feebly, “But I can’t imagine how you...”
Ellery had gone to the blondewood desk near the window and pulled a drawer open. Now he took out a card and glanced over it. “Yes. You traced the purchase of that poison, which bears the brand name of D-e-t-h hyphen o-n hyphen R-a-t-z. You discovered that this revoltingly named substance was purchased on May the thirteenth of this year at... let me see... at Kepler’s Pharmacy at 1723 North Highland.”
Laurel looked at Macgowan. He was grinning. She glared at him and then back at Ellery.
“You questioned either Mr. Kepler himself,” Ellery went on, “or his clerk, Mr. Candy ― unfortunately my crystal ball went blank at this point. But one of them told you that the can of Deth-on-Ratz was bought by a tall, handsome man whom he identified ― probably from a set of snapshots you had with you ― as Alfred Wallace. Correct, Laurel?”
Laurel said tightly, “How did you find out?”