The book opens with just another cool and calm day at Bayport where people don’t like such an action scene. A sinkhole in the ground just takes down one of the biggest statues in the city alarming everyone near to it. A sinkhole, of course, is not an impossibility but for the people of Bayport, it is something odd because the land of the town is not of that structure which would allow a sinkhole. Frank and Joe want to get closer to the spot to gain an idea of what has happened at the place.
They change their get-ups and get a fake identity for the mission and finally reach the base of the spot where the happening took place. Chasing clues the two Hardy boys reach an astonishing thing i.e an underground city. Not even the locals of the town have been aware of the fact that there exists an underground city under Bayport. Criminals have gathered in this city and they have been using it as their hideout for years. After years of planning those criminal gangs are ready to take over the city with their clever planning.
Hardy boys faced dangers in Shadows at Predator Reef and Deception on the Set but here they just land in front of the train ready to be squashed. During their perilous journey, Tim Gregory’s narration portrays everything well. Franklin W. Dixon has made his heroes stand against a whole army in this tenth part that’s why they look really scared at different spots. But they never give up when it comes to the safety of their town and the well being of its citizens.
