She addressed me without turning her head. "Marshall," she said, "please stand by the door. Nobody gets in until the nurse gets here."
I complied, standing with my back against the door, watching the suspects. They had, for the moment, lost any desire to ask questions or talk back.
"Let's start with this," she said to them. "Your classmate, Roger, has been poisoned. Until we figure this out, nobody should eat or drink anything. Now, do any of you know of a reason for anybody to want to hurt or kill Roger?"
"But it wasn't his cup of soda," Pete said. "It was mine, but I hadn't touched it. How could anybody have–"
"But it was Roger who–" Carol began, but my employer held up her hand.
"Wait, please," she said. "With any investigation, we start with motive, means, or opportunity. With this one, I'm starting with motive."
"Why?" Ms. Tumolo asked. "I would think–"
"Please excuse my interruption," my employer said, "but I will tell you my reason." I saw her shift her weight, and I knew this meant that her leg was getting tired. I abandoned my post for a moment and brought a chair over to her. I placed it behind her, and she extended her arm slightly, so I took it and helped her to sit down. She said, "Thank you," but she did not take her eyes off the suspects.
Returning quickly to the door, I noticed that Roger had rolled onto his back. He had one hand on his stomach, and the other arm across his eyes.
"My reason is this," she continued. "The question of means is easy to answer, at least for now. I don't know how many of you saw the box of rat poison in the kitchen, but I did. Opportunity is very difficult. There are several contradictory indications, as I'm sure you've all noticed. We will work our way through them in due time, but systematically and logically, not by interrupting each other willy-nilly. And I have some ideas about the question of opportunity, as well as means, but most of you are strangers to me, so I have no idea about motive. So, we'll start there, because that's where there's the most to learn.
"Motive, means, and opportunity, any one of the three can ruin a perfectly good theory that's based on the other two. So, who likes him, dislikes him, loves him, hates him–"