Just a random dream I had last night. Not a lot of detail on this one, but what is there is pretty cool.
Alien race bent on destruction of the entire galaxy lives in another 'realm' that connects to this through certain points in space - portals, like wormholes, to their galaxy.
We construct large platforms over the portals, a series of rings, each powered up. These emit a shield of energy that is harmful to the aliens, not killing them instantly, but seriously injuring them. They are harmless to humans.
We are used to defending bases from occasional assaults - but one day, they assault two nearby bases with great numbers, forcing each other through the rings til the first (there are two portals here, nowhere else are there two in such close proximity) and largest platform is disabled.
We live on stations - we're a mix of military and civilians, the civilians tending to everyday life while we protect them. They also help to maintain the portals. We manage to push them back from the largest platform, and I get it working again - then we discover they'd only let us push them back - the other station is overrun, the platform completely destroyed, our few suited military struggling to survive and fall back to our position.
I call the retreat to them - one of them refuses, continuing to fight until everyone else has fallen back to us and then gets overwhelmed.
We're now struggling to defend the second station and platform, calling for reinforcements.
Details:
We didn't have ships - we were never expecting to need them, since the aliens had never attacked in such forces before. A fleet was on the way, but we were stuck defending ourselves and the stations wearing powersuits, large bulky suits build for low-scale space combat. We didn't know how far out the fleet was, just that it was coming.
The two portals were not far away, close enough to keep tabs on what was going on at the other when not too distracted. The portal that got overwhelmed has a smaller station - the larger one was more easily defended as it had a lot more defences, which is why they let us push them back there, to take out the easier target while we were distracted.
The aliens looked insectoidal (vaguely Zerg-ish). They wore suits that gave them that appearance, that also functioned in a manner that made it appear real - we didn't know they were suits, they were seamless, had a glossy sheen, and moved so effortlessly.