Architect Doug Roberts returns to San Francisco after a business trip to attend the dedication ceremony of the one hundred thirty-eight story glass tower apartment and office building he designed for Duncan Enterprises. Met at the tower by company president Jim Duncan, Doug evades talk of collaborating with Duncan again in order to meet with his girl friend, editor Susan Franklin. As preparations proceed elsewhere in the tower for the evening’s gala celebration, a power generator overheats in the main utility room and burns through wiring. This raises concerns for chief technician Callahan and security head Harry Jernigan who notes that the security sensor did not automatically trigger the fire department alarm. Unknown to anyone, in a storage room on the eighty-first floor, a circuit breaker blows and sparks emanating from a burned out wire set fire to a pile of rags on a nearby cart. Meanwhile, Doug and Susan’s reunion is interrupted by Callahan’s supervisor, Will Giddings, who reports the wiring problems. Confirming that the material is not what was requested by his building specifications, Doug confronts Duncan, who refuses Giddings’ suggestion to postpone the dedication party until the building’s entire safety equipment has been completed. Frustrated, Doug goes to the home of Duncan’s daughter Patty and her husband, contractor Roger Simmons, whom he accuses him of using inferior materials in the tower, motivated by kickbacks. Meanwhile the press and public begin gathering at the tower entrance to watch the ceremony, which is led by Mayor Robert Ramsay and his wife Paula. Among the others attending the event are Senator Gary Parker, the Simmons, Susan, and elderly tenant Harlee Claiborne, who is escorting his neighbor, art teacher Lisolette Mueller. After Ramsay dedicates the tower as the world’s tallest building, Duncan Enterprises public relations head Dan Bigelow orders all one hundred thirty-eight floors lit up. As the three hundred party guests head up to the Promenade deck on the hundred and thirty-fifth floor, the fire in the storage grows, while the extra lighting places an additional burden on the generators. After angrily ordering the extra lights turned off, Doug and Giddings proceed to check electrical relays on the eighty-first floor. When Jernigan receives a report of smoke on the same floor, he manually sets off a fire alarm. After the men arrive at the burning storage room, Giddings tries to prevent an anxious guard from opening the smoking storage room, but the built up pressure of the fire blows outward, setting Giddings on fire. Jernigan then arrives and orders the eighty-first floor and the floors immediately above evacuated. Learning of the storage room accident from Doug, Duncan nevertheless refuses to relocate the VIP party from the Promenade deck. Fire chief Mike O’Hallorhan arrives with the first fire trucks and sets up his command center near Doug’s offices on the seventy-ninth floor, observing that it is virtually impossible to contain a fire in any building over seven stories. After checking on the fire on the eighty-first floor, Mike visits the party to insist on moving the guests to the ground floor. Returning to his command post, Mike learns from his assistant Kappy that the fire is in danger of spreading to other floors through the building’s main core shaft and the numerous over-sized outer windows. Upon hearing an explosion, the men discover that the fire has jumped several floors, prompting Mike to order the heat-sensitive express elevators transporting party guests to be halted and requests additional fire unit backups. Doug contacts Duncan to tell him to direct guests to the scenic elevator which runs on a track on the outside of the building. Worried about deaf neighbor Mrs. Allbright and her two young children, Philip and Angela, Lisolette, one of the first guests to leave the party, goes to their apartment on the eighty-seventh floor. Meanwhile, in the Promenade deck, guests are stunned when the express elevator, which has automatically stopped on a fire floor, returns carrying the charred bodies of the last group of party goers. Unknown to anyone, Dan and his private secretary, Lorrie, have been having a romantic rendezvous in Dan’s offices on the sixty-fifth floor and, unaware that the fire has consumed their outer offices, are trapped and unable to escape. Seeing Lisolette on the security monitor, Jernigan and Doug hasten to the Allbrights’ apartment. Discovering Mrs. Allbright unconscious from smoke inhalation, Jernigan carries her away, while Doug locates Philip and Angela. Cut off by fire from one stairwell, Doug, Lisolette and the children head down another stairway where they are caught by an explosion of a ruptured gas line. Although they are uninjured, the stairwell is destroyed, forcing Doug to slide down to secure footing on the dangling remains of the stair railings as the others wait above. Although able to convince the nimble Philip to clamber down the railings, Doug must climb back up to rescue Angela, then encourage Lisolette to struggle down on her own. Discovering a safe service elevator that originates on that floor and only goes up, Doug takes Lisolette and the children just below the Promenade deck, but finds its south entrance blocked by an overturned wheelbarrow of hardened cement. Now Navy Chief Flaker informs Mike of the arrival of air rescue helicopters, but admits that the winds are too high to land them on the tower’s roof. After Doug takes the crawl shaft to the roof and back into Promenade deck, Lisolette and the children are joined by firemen Scott and Mark Powers, who have been sent to dislodge the cement block with explosives. In the utility room, the master generator blows out and the back-up fails, cutting off most of the electricity in the tower. At the Promenade deck, Scott and Mark blow the blocked door and report that explosions several floors below have made the exit impassable. Despite their report, a frustrated Simmons declares his intention to take the stairs to safety, but is driven back moments later by an explosion and fire. Knowing that the power failure has affected the scenic elevator, Mike orders Flaker to set up a breeches buoy from the hundred-and-two story Peerless building next door, explaining that a helicopter can shoot a lanyard line into the Promenade deck. When weather reports indicate the winds have calmed, Flaker approves a rescue helicopter to make a landing to begin transporting guests to safety. After having the remaining guests in the Promenade deck draw numbers to designate their order of departure, the first group, including Susan and Paula, heads to the roof, but two overzealous women rush to the landing pad, forcing the helicopter to pull back, hit the railing and explode. Doug reports the disaster to Mike, who instructs him to have Scott and Mark prepare for the breeches buoy hook-up. As the firemen begin breaking the windows, Doug realizes that he can trip the scenic elevator gravity brake, which will allow it to make a single trip down. Placing the first group intended for the helicopter into the elevator, including a protesting Susan, Doug also adds Lisolette, the children and Mark. As Doug, Duncan, Scott, Parker and Ramsay assist in rigging the breeches buoy, the scenic elevator descends several floors before a nearby explosion buffets it off its track. As the elevator lurches sharply, Lisolette is thrown off balance, and while Mark wildly grabs Angela from her, he cannot hold Lisolette, who tumbles out of the elevator through the glass wall. When Kappy reports the latest calamity to Mike, Mike asks Flaker to have a helicopter pick him up on top of the Peerless building. As terrified women guests begin a one-by-one descent on the breeches buoy from the Promenade deck to the Peerless rooftop, Mike orders the rescue helicopter to carry him on a cable with a large crane hook to the top of the scenic elevator, which remains dangling by a single steel line. Once there, Mike and Mark attach the helicopter hook and cable to the elevator, but an explosion again goes off near them sending Mark slipping from the elevator top. Despite wearing heavy work gloves, Mike lunges for Mark and struggles to hold on to him as the helicopter pulls the elevator from the building and begins slowly lowering it down to the street. Even though Mark pulls off one of his gloves, Mike holds him single-handedly long enough for Mark to drop onto a safety net below. After a brief rest, Mike is summoned by the chief deputy, who informs him that they have ascertained that the fire will reach the Promenade deck in twenty minutes. A structural engineer has calculated that the building can withstand the explosion of five huge water tanks two floors above the room which would, theoretically, douse the fire. Incredulous, Mike realizes that he is the only surviving professional who has explosives knowledge and wearily agrees to return to the Promenade deck. Meanwhile, after the women all have been transported to safety on the breeches buoy, Simmons, who resents the selection process, incites several other men to rebel. As Doug is speaking to Mike on the phone, Simmons and his allies rush the buoy, and when Parker and others attempt to stop them, their combined weight pulls the small chair down, sending Parker, Simmons and other men to their death. Agreeing to help Mike set the charges, Doug then meets him on the roof, where Mike is dropped in a fire protection suit. Setting the explosive on a five-minute delayed detonator, Mike and Doug hurry back to the Promenade deck where they tie themselves down with the remaining men. The explosions release millions of gallons of water that crash through the ceilings down upon the men. Several men are swept away by the force of the rushing waters, including the mayor, but the majority, including Mike, Doug, Duncan and Harlee, survive and as the waters cascade through the tower, the fire gradually is snuffed out. Much later, Mike sees Doug and Susan outside the gutted tower and tells them that if architects learned to work with fire experts, they could at last begin to construct a safer world together.