I continued reading Nancy Drew Hardy Boys: Operation Titanic. In the rest of the book, Nancy and Bess go shopping and get ready for the Titanic cruise. And honestly, not much else. The billionaire gets flirty with her, and even though Nancy gets held at gunpoint in one scene, she really doesn't do much that's interesting.
Instead, the book focuses on the Hardy Boys. They have to save people from a sinking submarine, get chased by more hitmen with guns and meet with top secret government agents. Also, Joe keeps trying to make a move on a girl named Mandy, who shoots him down at every opportunity.
Eventually, The Gray Man (a government agent) decides to hire the Hardy Boys to work on the current case, seeing as they're knee-deep in it already. He gives them a simple assignment: identify a terrorist who is on the Titanic cruise. The terrorist is in disguise, but his bodyguards aren't, so it's not too long before they catch him. The Gray Man says they did a good job, then tells them to scram.
You can't get rid of the Hardy Boys that easily. They stick around for the rest of the cruise, and they spend some time with Nancy. Things get interesting again, when the mission to raise the Titanic gets underway. The terrorists attempt to seize control of the boat, and there is a lot of gunfire. Nancy and Frank team up to defeat the bad guys and save everyone.
Meanwhile, Joe is under the sea in a small submarine. Their goal is to help raise the Titanic, but Mandy reveals that she is secretly evil. So that's why she rejected Joe's advances! Mandy shoots everyone with a tranquilizer gun, then uses the submarine arms not to raise the Titanic, but to raise some nuclear missiles from the Gulf War.
Nukes which just happened to go missing, right where the Titanic sank.
Fortunately, it seems Joe has built up some immunity to tranquilizer. He stays awake long enough to fight Mandy and knock her out. He ruins the submarine arms (so they can't be used for evil), and he sets the submarine to rise to safety. Then he falls unconscious.
In the end, our heroes single-handedly stopped terrorists from getting the Titanic nukes. The complex plots to get the nukes (both by the terrorists and the government) is explained. Sadly, because this is a top secret mission, no one can know about it, so Nancy and the Hardy Boys get absolutely no credit for saving the world. What a gyp.