Idea for a scenario. Without the wargame rules in hand it's impossible to balance, but with minor tweaking this could probably work for any sci-fi skirmish or wargame rules set.
OUTBREAK
Forces:
Humans:
Four 5-man groups of unarmed scientists
Four 5-man squads of WY mercenary riflemen
One 5-man "death squad" with smartguns
One 5-man "containment team" with flamethrowers
Two sentry guns
Aliens (start):
One brood of 5 Stalkers
One brood of 5 adult Warriors
10x independent Facehuggers
Aliens (reserves):
Facehuggers
Stalkers
Infant Warriors
Adult Warriors
1x Alien Queen
Battlefield:
6'x4' totally covered by corridors and at least five large rooms (laboratories). Multiple levels/stories of terrain are encouraged. Remember that long, straight corridors will become dangerous fire lanes and build accordingly. The labs should be spaced out at least 12" away from one another, if possible.
Deployment:
The Aliens starting figures are placed in one laboratory, which must be wholly inside one table quarter. One science team and one mercenary rifle team are then placed in each of the other labs. The Death Squad is placed anywhere in the table quarter opposite the Alien deployment zone, and not within 18" of an Alien figure. The human player then nominates which lab contains the Queen, and deploys the containment team in that room. The sentry guns are placed last, anywhere outside the table quarter the Aliens are deployed in.
Notes:
It is assumed that the starting Aliens have already killed the former occupants of the lab the are deployed in and have triggered the alarm, putting the facility into lockdown. All doors on the table begin closed. They can only be opened manually by humans (touching the door, no remote access!) and may be torn down as usual by Aliens.
All human models may move freely once the game starts, they do not have to stay where they are deployed. Additionally, models may split off and become one-model units of their own. These may join or rejoin units by moving into coherency, however no human unit may ever contain more than five models.
The humans may not kill any Aliens (especially the Queen) that are still secured. They may only attack Aliens that have escaped and are already represented by a model on the table.
If the human player is feeling especially sinister, he may elect to execute the scientists to prevent the acceleration of the outbreak. Preform a normal shooting attack against the scientist unit. Any survivors will naturally flee if possible, and will now be controlled by the Alien player.
The Aliens objective is to make it through the other laboratories, releasing more of their kin as they progress and eventually freeing the Queen.
OBJECTIVE - Free the Queen and escort her to any table edge.
The humans objective is to stop the outbreak before it reaches critical mass, by any means necessary.
OBJECTIVE - Destroy all escaped specimens.
Outbreak!:
If the Aliens are for any reason alone in a lab (because they've killed everyone in it, or it was abandoned to form a strongpoint elsewhere, for example), all casualties to the starting units are replaced. Additionally the Alien player may deploy one of the following:
10x Infant Warriors + additional models equal to the number of human casualties inflicted thus far
5x adult Warriors + additional models equal to half the number of human casualties inflicted thus far (rounding up)
This rule may only be used once per lab, and does not apply to the lab the Aliens are initially deployed in.
Playing the scenario:
The Alien player gets the first turn, representing the sudden nature of the outbreak. The game ends when either the Queen moves into contact with a table edge or there are no Alien figures left on the table.