Trying to obliterate each other, two aliens capable of regenerating body parts that have been blown off, somehow both end up trying to convince a forensic pathologist that they are the good guy and that the other one is the trouble-maker. Which one? Well, exactly.
Similar in its plot to Dark Angel, but lucky enough not to have Dolph Lundgren in the oast. Two aliens, a serial killer and a space cop come to earth and chase each other around, pestering the coroner heroine by both claiming to be the good guy.
It's not hard to guess which of the aliens - a handsome hunk or shifty Robert Forster - is the baddie, but enough cars are crashed or exploded to make the enterprise reasonably worthwhile. There's also a bit of alien nookie, so I gave it an extra star.
If you're just starting out on a career in science fiction, don't begin with this.