 Construction magnate Jim Duncan (Holden) has teamed with architect Doug Roberts (Newman) to build a 135-storey structure named  The Glass Tower  in San Francisco. On opening night, many dignitaries including a U.S. Senator, San Francisco s Mayor & his wife and others are celebrating in the ballroom/restaurant on the top floor. On the 81st floor, in a utility room, an overloaded circuit breaker starts a fire in a can of oily rags. While the party is still going on, Roberts is inspecting the wiring in the building and discovers it is very low standard - a serious fire hazard. In the Security HQ, a guard, Jernigan (Simpson) spots smoke crawling out from under a door, and activates the alarm. The San Francisco Fire Department immediately comes out, with Chief O Hallorhan (McQueen) commanding. By now fires are starting all over the building, and the enraged Duncan discovers that his son-in-law, Simmons (Chamberlain) is the one who chose the cheaper wiring to save money. As the night goes on the fire races closer and closer to those trapped in the Tower, until the Chief discovers that detonating the water tanks above them will likely drown the fire - but will it kill the remaining men trapped inside?