The eighteenth story in the original Hardy Boys series (noting that my copy is of the 1960s re-write) surprised me by surpassing the quality of the immediately previous adventures by being an excellent story and a good mystery that I really enjoyed.

There are a number of tropes that recur from earlier stories, but something about this story, which kicks off with the boys being asked to keep an eye on a suspicious ship, comes together into a story which flows at a good speed, survives the test of time without being offensive or silly, and makes for a mystery that seems completely plausible.