This story never made it farther than being roughly planned, but here we are anyways.
Meet Annette. A young girl, maybe freshly out of high school, with short/wavy black hair, a love of mystery novels (and a critical thinking mind!), and a tendency to not smile. Annette is invited onboard the luxurious cruise ship named [NAME] for her wealthy Aunt's wedding. As the cruise ship leaves the dock far enough, it is discovered that her Aunt's new husband (her new uncle) has been murdered. The connections to the shore has been cut off (!!!), so the coast guard cannot be contacted until the employees get the channels working. So they're stuck on a boat with a potential killer.
But not to fear, aboard this fabulous boat is many luxuries that one could only dream to enjoy. Five star meals, in house entertainment, and workers tailored to make your trip as comfortable as can be, despite, y'know, the murder. Annette is suspicious, however, and starts stalking potential suspects, such as:
-The Captain, who seems to have anger issues
-The musician, who is /too/ friendly with her aunt after she complements his piano performance
-A maid, who was sneaking around her aunt/uncle's dorm
-The Chef, who is handy with knives and happens to be one of the only people with access to the kitchen knives (the uncle was stabbed and shoved into a barrel)
-??? Some other people, I guess
...basically as Annette investigates, more bodies turn up before she can prove anything or get more clues. Blah blah. The murderer is actually her aunt, because her husband is hella rich and she wanted his money. her aunt tries to kill Annette but someone pushes her aunt overboard. Lit. The communications get back online and they get back to shore safely. People complement Annette's investigative skills and she considers becoming a detective.