You are a headhunter. You hunt people down, kill them, decapitate them and then shrink their head. Except you're not some illiterate tribesman with a bone through your nose, and you're not out in the jungle somewhere, you're in the city. A futuristic dual dystopia/utopia city at that. The typical 'upper levels are paradise, lower levels are hell' type deal. And you're not headhunting to just collect keepsakes here. Something's going down, the whole city is in danger but the public doesn't know and the corrupt bureaucracy isn't going to do a damn thing bout it. In fact, no one is consciously aware of the threat, even those involved in perpetrating it. That's why you need their heads. With some secret advanced cybertech, you can extract information from the heads of those involved by turning them into cooperative 'guides' to help you find out the truth about the nature of the threat to the city. Which is why you have to shrink the heads. You can't exactly carry around more than the normal quota of full-sized heads inconspicuously. But if you have a shrunken one in your jacket and converse with it out loud people will just think you're calling someone over the net and not give you a second thought.