Having a gameplay objective is a fair thing to work with. However, either you need to have an overarching objective with suspense and tension (x amounts of days until event y happens), or have various roles on the server, and have yourself or other admins play as various villains.
Villain characters in a role play should have high health, have rather advanced operations, and have elaborate traps/settings/environments meant to create problems for the other roleplayers. Because of the nature of the role, admins would be best suited for it, especially with an add-on that hides the "observer" message so they can spy on players and play a more devious role.
You have to trust that these people would not abuse anything, and you could have villains that are non-admin, but it will be harder to pull off villain tropes, such as being everywhere at once (teleporting), and knowing too much (spying on other players).
Suspense and tension events should be set up beforehand, but pretty much have an "on/off" switch that any admin can pull. These all need to be set up beforehand. Examples of events are: alien invasion, days until military arrives for extraction, time until flood, time until volcano erupts, etc.
