Plans to Kill: Mystery? Thriller?

"I can't believe you told her you were planning on killing her." "I didn't exactly *plan* on telling her--it just slipped out!" "What, with the morning tea? Good morning, dear, anything interesting in the paper today, and oh by the way, I'm planning on killing you?" "Well, something like that, yes...." "Dear heavens. And what, pray tell, was the ladies response?" "She laughed and said that she'd poisoned the tea herself. Why do you think we're meeting in a hospital?" "And had she?" "No." "Ah. Well, perhaps we'll get lucky and she thinks you were just joking, as she was." "Although there is some trace amount of a biological agent that they couldn't identify." "What?!" "It may be contagious, that's why they're not allowing visitors." "And you sat there and breathed the same air--!"

Inspiration: Voices in my head. Except I forgot what they said, and so this happened instead.
Story Potential: Medium.
Notes: Meh.