Start with the timing. Harold was found dead at 9:40, and the poison kills within 15 minutes of being swallowed. That means he took his fatal sip somewhere between 9:25 and 9:40 — not at 9:00 when the scotch was poured. If he’d drunk it at 9:00, he’d have been dead by 9:15.
So the glass sat there for almost half an hour before he touched it. Why?
Because of Harold’s rule: he never drank alone. Daniel poured the scotch at 9:00 and immediately stepped into the hallway to take a call. Harold was left by himself with a full glass — so he didn’t touch it. He was waiting for company. The glass being three-quarters full confirms it: he took one or two sips, not a whole drink.
That gives us a very specific window. Whoever was standing in that study with Harold at roughly 9:30, watching him raise the glass, is the killer.
Margaret was in the kitchen with the caterer until 9:30 — a witness puts her there, and the poison was already in the glass before Harold drank. Daniel poured the drink but then walked away from it; if he’d poisoned it at 9:00, he had no way of knowing Harold would wait 30 minutes to drink, and he wasn’t in the room to keep the rule from stopping him. Thomas was on the second floor all night and never went near the study.
That leaves Ruth — the one person who walked directly into the study during the exact window Harold died.
And here’s the detail that seals it: her coat was still damp. The rain stopped at 8:30. A coat that’s still wet at 9:40 belonged to someone who walked in while it was raining — before 8:30. Ruth claimed she arrived at 9:15.
She lied about her arrival time by at least 45 minutes. That’s 45 unaccounted-for minutes in a house where a man was poisoned — plenty of time to get to the study, wait for the drink to be poured, and slip something into a glass nobody was watching.
Then she “arrived,” walked in to say hello, and gave her brother the one thing he was waiting for: someone to drink with.
ANSWER: Ruth killed him.
