I think I like the kid versions of the Hardy Boys more than the teen versions, somehow! Maybe because they get to play with puppies more? (I do still forget which one is which, though.)
The story proceeds at a nice pace to encourage younger readers to solve the mystery on their own, but the "main" case isn't really one that is possible to guess, since the "Why" isn't made clear until they find where the map leads and they question the reason for what they found. Though they have a little revenge on a certain bully... that's always nice.
The secondary mystery is a little easier to guess, but not by much. Again, it depends on information that isn't provided until the end.
Even so, it's a fun read, including the mini-comic at the end. Another great book for Hardy boys fans!