Here’s an idea that I used for a one-shot recently. It is, essentially, the movie Deep Rising tweaked for the Firefly universe. (It’s what I call a terrible-but-fun movie; have a look.)

The players are one of two groups — either the ship crew of a smallish freighter like White Lightning from the supplement Six-Shooters & Spaceships, or a group of mercenaries that have been hired to rob then destroy a fancy new passenger liner. If they are the freighter crew, they don’t know the actual score — they’ve been hired on a “if the cash is there, we do not care” basis, simply running the gun bunnies to point X in the Black and back. The mercs know the full score but are leaving the transpo guys in the dark for OPSEC.

The crew is hired one of the border moons or planets — whatever is easiest for your campaign. For a one-shot, you could have the action start on Persephone with Badger fronting the deal, or on Beaumonde with Mingo and Fanty. They’ve got a hard run out to a location in space that is a bit off the shipping lanes, but still reasonable. If they snoop about the cargo, they’ll find the gear the mercs brought with them includes 4 200 lb. (d6W) anti-ship (spacecraft scale) missiles with a launcher rig that can be mag-locked to the hull. What do they need with artillery?

A few minutes out from being able to find the liner, they should encounter some kind of debris — a lifeboat or shuttle — that they’ll hit before they eventually find the liner. Or if they have the usual cheap boat with bad maintenance, just hit them with some kind of failure. For whatever reason, they need safe harbor on the liner and won’t be able to run for it right off.

For the liner,  you could use El Dorado from the core rules or the passenger liner from SS&S; the bigger, the better — adrift and apparently on emergency power. The mercenaries knew this would be the case — they have an inside man (the owner of the thing) aboard who sabotaged her. The plan was simple: the ship suffers a catastrophic failure and after the passengers are offloaded, the valuables are pilfered, the ship destroyed, and the massive insurance claim filed. (The ship is so expensive, they’re running at a loss, even with a full-manifest.)

When they go aboard, however, there’s no one to be found. There’s indications of a hell of a fight — blood, bullet holes, but no bodies. They have to hit the vault, the engineering section’s machine shop to get what they need to fix their ship. Split ’em up. Lose a few NPCs who can disappear with some blood-curdling scream on radio. Eventually, they’ll have to find the bodies of the crew and passengers (maybe some still alive to make it more terrible) in a hold. There’s also something else, something worse — REAVERS!

There should be a lot of them, and it should turn into a run & gun, cat & mouse game to get back to their ship and get the hell out of there. Once they are off the liner, they’ll have to run for it, because the reaver ship that dropped the boarding party is coming back.

Tweak as you need to make it work for your game — change the scale of the opposition or the liner to suit your purposes — but it should be a good horror/action adventure for you to run.