Designing A Compact Mystery

[J. A.]

I could use some advice on how to structure the plot of a scenario I’ve been working on. This will be based at a country estate, and it’s intended as a one- or two-session adventure for starting characters, with an emphasis on amateur sleuthing.

The essence is that Something Important has been stolen, and the estate is in an uproar trying to find it. The thief, who is a member of the estate’s household, has hidden the SI in such a way as to implicate another member of the household.

So, I have the scenario, but I’m not sure how to translate this into a working outline to run a session. The PCs will be employees of the estate, but they won’t have any resources other than their own ingenuity.

Where do I take it from here?

[ErichAD]

The general order of events you need is this:
-The players discover that the theft was committed for a reason other than to steal the item.
-Another party discovers the planted item but doesn't know that the item was planted.
-The party intervenes on behalf of the accused.
-The party discovers proof of the real culprit and exposes the plot.

All of these events are required, so focus on degrees of success for each event. If you allow one event to solve another event, then the story will miss your archetypal plot beats. That's fine if you don't mind, but I imagine you do somewhat.

As a broader guideline.
The players know the accused couldn't have or wouldn't have committed the crime but can't say exactly why or what they know. Perhaps they're sworn to secrecy, they were committing their own criminal act while witnessing the proof, or they can't explain what they saw because they don't understand it.
The second party discovers the planted item and is taken in by the ruse, or are in on the plot to frame the apparent criminal.
The party can plead on behalf of the accused to have them held at the estate rather than turned over to the cops, they can plead for them to be left free and the house put on lock down so that everyone is treated equally in the investigation, or they can hide the accused till the figure out who really committed the crime.
The party could extract a confession from the real criminal, trick them into revealing themselves, straight up lie to convince others that a different party is responsible with no proof, discover further evidence of the planting and cover up.