I've got a D&D plot that I've worked out and tried to run no less than twice, but circumstances prevented it. (The party didn't go the way I hoped and the group just was too flaky due to responsibilities and we basically never actually had sessions until we all admitted it was a lost cause.)

If you're familiar with Eberron, that's what I planned for the setting. Settle in, because this is going to be pretty long.

A profit-hungry middle-management asshole named "Wallace" at a magical R&D lab hires the party to clear some hostiles out of said lab, but can't risk unlocking the door and letting the hostiles out. He tells the PCs is that his plan is to have the PCs "remote pilot" some drone units that are in the hostile-controlled area. They'd be able to use the drones to kill the baddies.

In actuality, they're not remote piloting anything. The devices they were told were just controllers are actually consciousness copiers. And the PCs' consciousnesses are copied into Warforged bodies in the hostile-controlled area. The PCs take out the hostiles and, task accomplished, ask to be disconnected from the controllers. Wallace copies their consciousness back into their flesh bodies, still without telling the PCs that it wasn't just a "remote piloting" kind of situation.

Wallace is incompetent and due to an error on his part, the copies of the PCs' consciousnesses are still active in the Warforged bodies wondering why they haven't been disconnected from the controller yet. And why Wallace isn't answering on the sending stone.

Furthermore, this consciousness copying technology is still in alpha and so new that Wallace doesn't know the fatal flaw: that a consciousness can't really persist in not-its-own body for more than a few hours without going basically Joker levels of criminally insane.

After the PCs have collected their payment and gone on their way, Wallace, thinking it's safe, unlocks the doors to the previously-dangerous area. And there are the PCs' clones in Warforged bodies. Angry. Unhinged. Babbling about how uncontrollable is their urge to rend Wallace limb from limb.

And then the Warforged notice their flesh bodies are... missing. And Wallace isn't giving any straight answers about anything. And the fact that Wallace hasn't paid them yet sure doesn't fucking help the situation.

They end up brutally murdering Wallace. Others in the same office building hear screams and call the authorities. When the city guard show up, the murderous robots are still taking turns pummeling Wallace into an even thinner pink, pulpy smear. The authorities manage to arrest the Warforged PC clones. When the authorities ask the Warforgeds' designations, the Warforged respond... with the PCs' names.

Meanwhile, all the original flesh PCs know is that they did a job for a guy that involved some cool remote-piloted drone technology, got paid, and went on their merry way. But the next morning the newspaper says that that Wallace guy was brutally murdered in his R&D lab only a few hours after they last saw him. So they go back to the R&D lab where the cops are still combing the area. When the cops find out the flesh PCs' names (the same names the Warforgeds gave), they immediately take the PCs back to the station in irons for questioning as "persons of interest" in this bonkers murder case.

While the PCs are shackled and being questioned at the station, the evil Warforged clones break out of the adjoining prison causing unholy chaos just outside of the interrogation room and escape, killing the only cop who knows the PCs and the Warforged shared the same names in the process. After a while, another cop, thinking the PCs are just there for poking around too much at a crime scene lets them off with a warning.

But now the murderously evil Warforged are loose and want nothing more than to steal back their bodies via whatever means necessary. Or, as a consolation prize, maybe just murder the PCs. And by this point in the story, depending what questions the PCs asked the cops and how good their persuasion and insight rolls were, the PCs (and players) may well still be a little confused as to what all exactly is going on. So they may have some sleuthing to do. Once they know what's up, the PCs have the option off asking the cops for help, but that may well implicate the fleshy PCs themselves.

From there, my plan was for the evil Warforged guys to be basically long-running BBEGs. They'd level up along with the party but as twisted mirror images of them. And the party would have to seek them out or somehow lure them into traps and take them out one-by-one. How that all would play out would depend on how the fates went.