Titanic begins deep under the ocean (over two and half miles below the surface). The dark blue surrounds the camera's view, and then a light in the background appears. Several small submarines move in the darkness (reminiscent of Cameron's The Abyss) and the light shines upon a "ghost ship coming out of the darkness." What's so remarkable about this scene is that these shots are actual footage of the real Titanic. Cameron shot this footage, taking shots from inside the ship with small vessels attached to cables. The head of these excursions into the Titanic is led by Brock Lovett (Bill Paxton), an explorer hoping to find a valuable diamond which was believed to be aboard the ship. Instead of finding the diamond, they find a safe full of drawings and other rotted paper. One of these drawings is of a nude woman, who happens to be wearing the diamond, appropriately called The Heart of the Ocean.
Showing the picture on the TV, Lovett receives a phone call from Rose Calvert (Gloria Stuart), who claims to be the woman in the picture. She is flown in, where she begins to tell a story about a woman, Rose DeWitt Butaker (Kate Winslet). Rose is a 17 year old girl being forced to marry a man she does not love. This man is Cal Hockley (Billy Zane), a rich eccentric with more love for his money than Rose. Calvert's story begins with these two arriving at the farewell of the R.M.S. Titanic, nicknamed "The Unsinkable." The first class members board with pets and luggage, while third class members need to be checked for lice and other diseases before boarding. A poor artist, Jack Dawson (Leonardo DiCaprio), wins a ticket for third class during a poker game. His friend, Fabrizio De Rossi (Danny Nucci), also boards in order to escape to America. Shortly after the ship leaves the dock, Jack spots Rose standing on the first class level. Rose is so miserable with her engagement that she runs to the edge of the boat to commit suicide. Jack stops her, and the two begin a friendship which later turns into a passionate affair.
