From this description, you might guess the ending of the story. Or maybe not.
As The Tenth Victim commences, American hunter extraordinaire, Caroline Meredith (Andress) makes her ninth kill, luring her "hunter" to the Masoch Club and then -- during a striptease -- murdering him with her double-barrel brassiere gun.
As is the case with other movies of concurrent vintage, such as ZPG (Zero Population Growth), Westworld, THX-1138 and Zardoz, The Tenth Victim predicts a future world in which governmental efforts to help solve a problem in fact succeed only in creating a corrupt new regime and civilization.
In The Tenth Victim, a hunter decries new Big Hunt regulations in Rome which prevent gun-men from opening fire in restaurants, hospitals and "nursery schools." Caroline responds proudly that such restrictions on personal freedom have not yet been approved in America, and Poletto shakes is head and notes, simply, that "America is...something."