Basically, you're an inventor's son and you've taken up the profession yourself. You fight evil "hackers" attempting to take over the world, and generally help out your hometown by building inventions for them and rescuing their children. This is as far as I've progressed, so I know there's quite a bit more to it. The overworld map is a bit unique, unlike some RPG's where you can walk anywhere and initiate in random combat, the overworld map in Robotrek seems more like the map used in Super Mario World.
I've played it for several hours now, and I'd suggest that if you like old-skool RPG's you give it a shot, you might like it. I tend to be a bit picky with my RPG's, but this one has me coming back for more. :-)