Carson Drew has a friend in trouble (again). Mr. Gonzales has a crocodile farm in Florida, and some of the workers seem to be acting rather shady. Mr. Gonzales needs help NOW, so of course, Mr. Drew enlists Nancy!
Nancy, George, and Bess fly to Florida to stay with the Cosgrove family. Big mistake! A man named Steven meets them at the airport to pick them up in his car, and suddenly Nancy, Bess and George are captives. Aready.
Nancy picks locks with the nail file and bobby pin she just happens to have. Very McGyver! Nancy, Bess and George run through a swamp eventually get back to civility so they can call the police; the police come to get their story, and Nancy, George and Bess take a cab to the Cosgrove's.
The gang visits Crocodile Island to meet Mr. Gonzales, who thinks his partners might be selling boot-leg crocodiles (WHAA?). When Nancy, Bess, and George try to visit Croc-Isle off-hours with the Cosgrove's son Danny, they are threatened by a man who man makes his point by scraping their boat with his, saying the damage will be worse if they don't get out fast.
After a mysterious nighttime delivery to the island and some threatening phone calls, things are getting scary. A.k.a, normal. Carson's worried, but Nancy convinces him that she can stay. After all, she has a sixteen-year-old boy (Danny) to protect her and her friends! She'll create a plan to keep herself from getting killed, too.
Nancy and Co. find treasure, look for clues, get attacked by mosquitoes, and discover that a suspect is an AWOL Navyman. They overhear a phone conversation; "...need five hundred" Five hundred what? Five hundred high-speed cameras from the US, that's what, smuggled out for secret operations! Freaky. Eventually, Nancy gets captured again, but not alone!
Nancy and Ned, who is visiting with Burt and Dave, get trapped in a submarine. Dave manages to radio for help. Everything is solved! No more sneaky camera operations. Everyone's safe, even the crocs.
- When Nancy wants to know more about submarines (she and her friends see a periscope in the water) she is able to visit a naval base, as the Cosgroves are, conveniently, friends with a naval captain. Nancy tracks down the AWOL. Really, this is much like The Mystery at the Moss-Covered Mansion: Florida, sneaking around the government, swamp animals threatening them...