This is the classic tale of how a cruise ship gets upended and a scrappy band of everyday people have to put aside their differences to survive. I reviewed a very similar Sylvester Stallone movie a while back. The difference between The Poseidon Adventure and that other movie is that The Poseidon Adventure didn't completely suck.
The movie starts out with the annoying little boy learning as much about the ship as he can. He's a typical annoying little boy. He meets the captain of the ship, played by Leslie Nielson (back when his hair was Steve Martin white). Annoying Boy has a sister, too. The two of them are going to Greece to meet up with their parents. There's also the old Jewish couple, Manny and Belle Rosen. Belle is a former swimmer, and Manny is, well, he loves his woman. Then there's another guy. I'll call him Charlie. Charlie is a closeted homosexual. There's also the Folk Singer whose brother dies, the Surly Cop, and his Whore Wife. Finally, there's Gene Hackman as Reverend Moon. I forgot his name, too. Gene Hackman is a hardass priest, and he firmly believes that God wants people to get off their asses and take control of their lives instead of sitting around, waiting for something to happen.
You've met the cast; now it's time for the plot. There's a big oceanic eathquake, and it flips the ship over. So, a bunch of people plummet from the floor to their respective deaths, and the rest of them are all stuck on the ceiling, trying to decide what to do. Gene Hackman takes charge, and he decides that they need to get as high as they can to the bottom of the ship. Meanwhile, another guy I'll call Uncle Bob decrees that they should just wait there until help arrives. Most of the people agree with Uncle Bob, since Uncle Bob actually works on the ship, and who the hell does this priest think he is, anyway. Well, Gene Hackman has convinced a ragtag group of ne'er-do-wells that they should go, so they start moving up. Once they get up to the next level (with a little help from a metal Christmas tree), the deck they were on just before gets flooded. All the naysayers scramble toward the fake tree and try to climb, but it tips over, and they all drown because they're big idiots who deserved it.
So, Gene Hackman leads them through the ship with a little help from one of the bellhops (who dies pretty quickly), and Surly Cop constantly disagrees with him just to be difficult. Charlie and the Folk Singer fall in love, proving that he's at least bisexual. Annoying Boy's sister develops a thing for Gene Hackman. Everything's looking up as they make their way through upside-down rooms and ventilation shafts. Pretty much every sequence they put in this movie was remade for Daylight, and I couldn't help but be reminded of that horrible horrible movie.
Eventually, they make it to the engine room, no thanks to Surly Cop, who wants to go the other way. By the time they get to the engine room, however, Belle Rosen has died trying to save Gene Hackman. But they must move on. They're almost there. Suddenly, there's a big explosion, and Whore Wife plummets to her ultimate demise. Suddenly, this is all Gene Hackman's fault. He killed Mrs. Rosen, the bellhop, and Whore Wife. It's all him. He's a murderer. If he'd just let them stay, they wouldn't have died. Well, they would have, but Surly Cop would have been dead, too, and he couldn't complain anymore. So, Surly Cop is tearing Gene Hackman a new one while Gene Hackman is hanging for dear life, trying to shut off the steam valve so they can all get to the bottom of the ship to be rescued. Gene Hackman tells Surly Cop to shut the hell up and take the people the rest of the way, cuz he's about to fall and die. Then he falls and dies.
So, Surly Cop takes whoever's left, and they find the bottom of the boat. They start hitting it a lot, and the rescuers cut through, and everyone is saved. Well, by everyone, I mean the people who aren't already dead. In other words, of the thousands upon thousands of people on the boat, six people made it.
I gotta say I liked this movie. It was pretty darn good. But I'm never going on a cruise.