I imagine Mind Merchants would work well but it does have an open ended ending which may feel a like a let down to some players as a one shot.
If you’re going to get it into four hours I’d suggest having the players find their weapons as soon as they escape the cage. I had the breakout and fight the guards for their weapons and it really slowed things down. I think it might work well with the right players but it killed the momentum with our game (though we all had loads of fun).
Modiphius have a version of Mind Merchants on their YouTube channel which runs in under four hours, that might be worth a look.
If you’ve got the Narrator Screen then the adventure builder looks pretty good (I know the Conan one was great).
I haven’t run the adventure at a convention at all, though I have run it on one of my gaming groups as a test scenario for the game back when it was still in Beta, but…
“Mind Merchants of Mars” would likely work pretty well for a convention scenario, but there are two provblems with it. First is the fact that it’s an open-ended scenario, meant to be the first salvo in a campaign. If I were to run it for a convention, I’d want to give it an actual solid ending so that the players weren’t feeling left down by the ending to what would really be a one-shot, rather than a campaign entry point. Second, the fight to escape the guards at the beginning could take longer than is best for a 4-hour scenario, especially since you also have to spend say 10 minutes explaining the game rules and mechanics.
Virginia of Modiphius ran “Mind Merchants” on the in-house gang at Modiphius in a set of four, roughly one-hour videos over on Youtube. I know that I plan to borrow the set-up and basic plot she ran for my campaigns.
That said, another option would be to write a scenario for a convention game. The adventure generator in the Narrator Toolkit might be good for doing this. I’ve already generated a couple of basic stories for my gaming campaigns this way.
The Quickstart scenario is actually one that I ran at CanGames 2018, and it worked rather well in the 4-hour slot. You’ll actually have about 3.5+ hours to run it, given that you need to go over the mechanics with the players and especially the Momentum, Threat and Luck rules.
I ran it twice at the convention, once with the characters from the novels, and once with characters that I created myself at the time using some scatterbrained ideas I had (since the early version of the character creation rules were a bit different). Worked fine.