Are you seriously crying already? The movie hasn't even started yet.
The movie starts out in the present day (well, present day in the dark ages of the 1990s). A guy named Brock Lovett (Bill Paxton) is heading up a crew of people searching for some kind of treasure in the wreck of the legendary Titanic. During one of the dives, he thinks he's found it, hauling a safe up to his boat and making a big ceremony out of opening it…
However, when he opens the safe, there's nothing inside. Lovett and the crew are bummed out, of course, but they do find a drawing of a woman apparently wearing what he's looking for: a very large diamond (and nothing else: yowza).
Lovett ends up on the news talking about his hunt for the diamond and the discovery of the drawing. An old woman sees him and gives him a call—because she's the woman in that drawing.
Not everyone in Lovett's crew is convinced the old woman is telling the truth, but they fly her out and on to the ship—presumably in case she knows where the diamond ended up after the sinking. Once she's all aboard, she settles in and tells them the story of her trip on the Titanic…
While a lot of her fellow passengers on that ship were pretty hyped up to sail on the "unsinkable ship," she was in a major funk when she boarded. It seems she was not looking forward to going back home and marrying her beau, Cal (Billy Zane). She was traveling with said fiancé, his valet Lovejoy (David Lovejoy), and her mommy dearest.
While the audience sees young Rose getting dragged onto Titanic, a guy named Jack is playing in a poker game—and tickets to get on the Titanic are in the pot. He wins the game on a full house, and so he and his friend Fabrizio have to rush to make it in time—but they get on board.
It turns out that the Swedish dudes who lost the poker game ended up winning…their lives.
Rose and Jack meet when Jack comes upon Rose trying to work up the nerve to throw herself off the back of the ship. Yes, that's how miserable she is. He succeeds in convincing her to come back over the railing, but she slips in the process. Jack hauls her back on board, landing on top of her—and of course, this is when other people come upon them and entirely misunderstand the situation.
A crowd gathers that includes the crew, Cal, and Lovejoy, and Rose is (of course) reluctant to explain what she was actually doing. However, as the crew prepares to detain Jack for trying to assault her, she manages to come up with a story about how she leaned too far overboard staring at the propellers, and Jack saved her.
As a result of all this, Cal ends up inviting Jack to dinner with them as a thank you. Lovejoy, however, doesn't seem convinced that Jack is the big hero everyone is making him out to be. In fact, he seems to have taken an immediate dislike to the boy.
And hey, fair enough, since Jack quickly ends up stealing Rose's heart away from Lovejoy's boss. He takes Rose dancing down below deck with the other steerage passengers, draws her nude in her suite (resulting in the drawing that Lovett finds many years later), and then they end up getting frisky in the cargo hold, in the backseat of a car (proving that people have been sexing in the backseats of cars since cars with backseats were invented).
When Cal realizes what's happening, he's super unimpressed.
Meanwhile, as all this love drama is going on, Titanic is having her own woes. In an effort to make a big "splash," the ship's powers-that-be had agreed to speed the ship up and reach New York earlier than expected. That would have been super impressive...
However, that extra speed makes it a lot harder to spot icebergs in time to do anything about them, and so Titanic ends up smacking into one. Unfortunately, that creates enough damage that the ship's builder, Mr. Andrews (Victor Garber), realizes that Titanic is definitely going to sink in an hour or two, despite the crew's best efforts to save her.
Evacuation efforts kick into gear, but they're pretty disorganized and favor the richer passengers. Lots of the steerage passengers end up locked below deck as the water flows up through the bottom of the ship, and the crew loads lifeboats pretty sparsely—wouldn't want to overcrowd the posh folks, after all.
As the boat sinks further and further, and it becomes clear that most people aren't going to make it into a boat, panic sets in. Despite her indiscretions with Jack, Cal makes an effort to get Rose and leave with her.
Rose and Jack don't make it onto lifeboats, and so they go down with the ship—literally. However, they manage to avoid drowning, and they find a door that Rose can float on (apparently, it can't withstand both of their weights). They wait for some of the lifeboats to come back for them once the sucking motion of Titanic's sinking dies down, but that takes a lot longer than expected.
When a lifeboat finally comes back to look for survivors, it appears that most people have frozen to death in the water. Rose is still alive, but apparently a little delirious, and she becomes extremely agitated when she realizes that Jack has frozen to death in the water beside her. She appears almost ready to give up, but then she remembers that she made him a promise to keep going no matter what—"I'll never let go, Jack!"—and so she manages to get the attention of the lifeboat that returned.
When she makes it to New York on the boat that picked up survivors, she gives her name as Rose Dawson as a tribute to her lost love.
Back in the present, Rose's story seems to have made an impact everyone listening, even Lovett, who had previously just treated the Titanic as an opportunity to look for treasure rather than a tragic story of human loss. He seems ready to abandon the search for the Heart of the Ocean.
Which is ironic because—surprise—it turns out the diamond is actually on board with them. Rose has had it all this time, since Cal stuck it in the pocket of a coat he gave to her to keep her warm during the sinking. After telling her whole story to Lovett and company, she sneaks out of her cabin in the middle of the night and drops the diamond off the side of Lovett's boat.
The movie ends with Rose apparently dying in her sleep, surrounded by photos of the adventures she had after the Titanic trip, and being reunited with Jack (and other dead Titanic passengers) in the afterlife.
Okay, it's acceptable to be crying now.