At the outskirts of New Orleans a sewage tunnel caves in; city officials are less concerned about the worker who was killed then about possible repercussions on the impending Mardi Gras in the French Quarter, which is the tourist hight point of the year in Louisiana, so the priority is to prevent a panic. Still Allison Beauchamp, under whose responsibility public works fall in city hall, calls on her intimate friend, geologist Matt Andrews, who is extremely cautious since an accident only he blames himself for, to investigate. Shortly after another cave in, he finds and reports -even arranging radar material was opposed by the Mardi Gras lobby- that such sink holes are caused by the lingering on of a fire in underground tunnels trough peat layers, so there's no way of telling where and when more sink-holes will collapse, but it may happen all over the city, and two million tourists joining in the reveling increase the risk, so everyone is in danger. However city press secretary George Regan, who knows mayor John Lafitte would probably follow her advice to evacuate, falsifies the report so Allison allows the Mardi Gras committee to go ahead with the annual festivities...

Mardi Gras in New Orleans shot in Toronto in December!

Errors in geography: New Orleans is below sea level resulting in a high water table. If you dig a hole a few feet deep it will likely fill with water. Yet in this movie the tunnels are 60-feet below ground and are bone dry despite being well below the water table.