In one of the early missions (the third one, maybe) your new employer wants to see how well you shoot your gun.

On the third trial he asks me to aim at the car, press the middle mouse button, and shoot the tired.

The middle mouse button does nothing. I have tried three different mice, and none of them make it work. (My middle mouse button works fine, just an act of desperation)

There is nowhere in the options to change this.

I like this game, it feels like it is worth the $3 and change I spent on it in Steam, but I can't get past this part.

Any ideas?

I'll answer this nine years late if anyone is having this problem. When you go to character controls you can go down with your arrow key to see the other page of the settings. I changed the free aim key to my keyboard and after assigning my center camera key I got it working.