In May of 1911, Molly Brown throws a sixteenth birthday party for Rose Walsh McLean, where she meets Cad Carnegie. On the Fourth of July, Cad asks Rose to marry him. Their engagement lasts until April of 1912, when the wedding party is returning from Europe on the maiden voyage of the R.M.S. Titanic.
Here, Rose meets a handsome steerage passenger named Jake Lawnsan, who persuades Rose to leave her world of high society. She makes the life-changing decision to stay with Jake while the ship sinks in the North Atlantic. She returns to America aboard the rescue ship Carpathia with Molly and the Blue Heart Diamond necklace in a pocket of her overcoat.
Many years later, Rose sees a news broadcast about an excavation of the Titanic. Sensing that the expedition has something to do with the necklace, Rose contacts Brice Buhaven, the head treasure hunter, and finally tells her story.