This story started here.
"What about the weapon?" I asked.
"One of the knives from the kitchen." She shook her head. "There were fingerprints on it, but that isn't much use until we have somebody to check them against. And even so, a lot of people use those knives." She turned to our daughter. "Ron, I need to ask you about your sister's underwear."
"You saw how she was dressed. Quite ordinary: sweater, skirt, sneakers, and socks. But her underwear was very racy, almost nonexistent. Her knickers–"
"Aaaah!" Ron protested, looking like she was about to plug up her ears and hum as loud as she could.
"Maybe it would be helpful," I suggested, "if you explained how this will help solve the mystery."
My employer shrugged. "Alright."
Jan Sleet was, in her private life, very unlikely to discuss anybody's underwear. But, when there was a mystery to solve, she would, with clinical detachment, happily discuss anything that was relevant, including sexual preferences and habits, and even, in one case, the specifics of a suspect's anatomy. So, she found it rather peculiar that Ron was reluctant to discuss something as comparatively innocuous as her sister's underwear.
"The question, Ron," she began, "is why was your sister here?"
"In that moment when you saw her," I added, "you thought she might have come here to ruin your life with us."
My employer nodded. "Possible, but unlikely. We do need to try to find out if she came alone. But the fact that she was wearing exotic lingerie, especially if that was unusual for her, could indicate a possible liaison."
"She could have been coming here to meet a lover," I explained.
Ron shrugged. "I always did the laundry," she said. "I never saw anything weird."
"Did Tracy have a boyfriend? Or a girlfriend?"
Ron shook her head. "She likes boys. Not girls. I don't know if she was dating. We didn't talk much."
"She never brought anybody home?"
"Not when I was there."