When a sinkhole opens up in the middle of town and swallows up one of Bayport's historic statues, the Hardy Boys suspect that something shady is at play. Joe and Frank discover an entire underground city that's been abandoned for years, but now that secret city is home to a cultish band of criminals who plan to take over Bayport. Can Frank and Joe thwart these crooked plans? Recommended for ages 9 to 12 years.
