Something is amiss in Bayport, the Hardy boys’ home town. First, there is
trouble in Shantytown, then a strange black craft tries to ram Joe and Frank’
boat, the Sleuth. That night the local bank is robbed. And later that same night
the young detectives’ pals, Chet Morton and Biff Hooper, mysteriously
disappear after a masquerade party.
Are the events related? And do they emanate from Shantytown—or from
Hermit Island, an isolated land mass inhabited for many years by a strange
recluse? Is it significant that both the missing boys and the bank robbers wore
masquerade masks? Or is it more important that Chet was wearing a costume
identical to Frank’s?
One by one, Frank and Joe tackle the clues, hardly daring to think what might
have happened to their missing friends. But it is not until the two brothers
confront the kidnapers that the overall pattern begins to emerge. The kidnapers
ruthlessly plan to force Frank and Joe’s famous detective father into choosing
between justice and his sons!
How the Hardy boys use all their courage and skill to outwit the criminals
provides an exciting climax to one of the most baffling mysteries the young
detectives have ever encountered.