"The game opens with an introduction video sequence of Duke riding his motorbike towards the Bootylicious Strip Club in downtown Los Angeles, only to find "Pig Cops" teleporting in to disrupt his fun, turning his motorcycle into a pink child's bicycle. Duke takes out the Pig Cops and the game begins. The video sequence is accompanied by the song "The Thing I Hate" by Stabbing Westward.
The first stage of the game is a hub stage. It is an "inner city" composed of the strip club, a subway, an apartment and manufacturing plant. On each visit to the hub stage, the appearance and enemies change slightly, and the dancers in the strip club change from women to mutated pigs and even men, resulting in humorous comments from a disgusted Duke. The objectives of the hub stages are to find 3 key crystals (hidden in a different location each time) and use them to operate a Time-Space Warp that Duke must use to travel to the Old West, Medieval Europe and Ancient Rome. In each scenario, Duke finds evidence of the aliens and pigs in period dress attempting to change history in their favor. Duke encounters several stages of action before a final confrontation against an enormous end boss. This game was followed up with Duke Nukem: Land of The Babes, and a game was made for the Nintendo 64 called Duke Nukem: Zero Hour which had a similar but considerably different plot."
Source: Wikipedia, "Duke Nukem: Time to Kill", available under the CC-BY-SA License.