Okay, so groundhogs day concept: like, the whole doing the same day over and over again, ending with being murdered at the end of the day. Standard stuff, except, it's a writer.
Specifically a writer who writes murder mystery novels. The first time they get killed they think it's a hallucination since yknow, they've been on a writing binge and hardly slept and they keep waking up to find they've fallen asleep at their desk/nook/half-hazardly arranged corner, so they don't think anything of it.
Second time they think it's a dream but get immediately distracted looking up if that was a valid way to kill someone and if they could write it into their novel.
By the third time they're more suspicious, but honestly weirder things have happened to them, and this wouldn't rank the top 10. Only, they've had to reschedule the same meeting they've missed three times now, or at least, they thought they missed it. They also thought they'd already rescheduled it, but they've also had multiple times they've been so anxious about something that they scripted and re-scripted the conversation in their head until they end up convincing themselves it's already happened.
Fourth time they've figured it out because they accidentally faceplanted the door and know they don't have magic healing powers (debatable) so when the bruising and black eye is gone the next morning, they know shits weird. Only this next time they're prepared. With questions.
They're writing a murder mystery novel after all, and what better way to gather information than straight from the source? Long story short, the writer hounds the killer with questions, asking things like "how would you prefer to kill someone?" "How long would it take to die if you stabbed someone like this?" "If you wanted information, what methods would you use?" It gets to the point the killer is kind of just letting the writer go on a rant about it. Very hesitantly offering up info here and there when they can get a word or two in