Following Alien Attack:
A similar smallish number of aliens is in the area, doing something that isn’t immediately threatening or deliberately dangerous.
Exploring, taking resources to a non-cataclysmic degree, fighting a non-human enemy who happens to be in our solar system, fixing their engine after an asteroid strike, looking for an escaped convict, shopping for trinkets or the local delicacy known as beef, whatever they’re up to attracts Skywatch’s attention. It could be indirectly dangerous to humanity, temporarily or permanently, or could inadvertently lead to danger, perhaps due to the attention it draws from the RAF and the like.
This may lead to misunderstandings on both sides, escalating threats, teaming up against other human or alien presences, an alien PC joining the group...
A four-strong Sodam science team arrives near the Skywatch base to investigate power fluctuations above humanity’s supposed tech level, caused by an item kept in the base’s vault. They travel invisibly, nosing around the base and looking at everything, leading to suspicions of gremlins, poltergeists or something stranger still. If the team work out how to detect them, they could capture one - which would bring the others out to rescue him at blaster-point.