I was one half of a young couple dressed in 50s type clothes fighting with another couple who we knew were evil alien imposters

At the end the man smashed up the evil alien man and there was red light everywhere and inside his head was a spider-like thing which he killed.

I had already killed the female.

And the red light stuff was radioactivity coming out

The galactic emperor was alerted that his agents had been destroyed, and they landed in a huge ship and two enormous robots got out and were looking for us over the top of the buildings