The Hardy's guided the motor boat out into the shark-infested ocean beyond the reef. Several times they saw sinister looking fins knifing through the sea around them. Suddenly Frank's blood ran cold - water was starting to pour in through a hole in the hull. They were sinking fast....... In the sultry heat of the West Indies, Frank and Joe hunt for a desperate gang of cargo thieves. But as the net tightens around the crooks, their tricks get nastier....

A lost gold mine...... Frank and Joe Hardy rescue a man injured in a shooting accident. Can his strange story of lost gold help solve the robbery case their detective father is working on? The Hardys leave for the old mining town of Lucky Lode - but a deadly trap is set for them on the way. Someone in town is in league with their enemy. Is it the friendly storekeeper? Or the mysterious businessman?

Camped out in the Maine woods, the Hardy boys get a real jolt when they glimpse Joe's old girlfriend, Iola Morton. Can it really be the same girl who was killed by a terrorist bomb? Frantically searching for her, Frank and Joe are trapped in the lair of the most diabolical team of scientists ever assembled.

When Frank and Joe are invited to join their Uncle Hugh for lunch, the main course turns out to be a bizarre kidnap plot. After a violent scuffle, Uncle Hugh is whisked away, and the boys suddenly find themselves in deep trouble with a government espionage team.

Where is Biff Hooper? The Hardy's friend secretly went off to survival camp in Georgia - and never came back. But before leaving he did tell Joe. So when Orville Brand, the camp director, claims Biff was never there, the Hardy boys suspect foul play.

When Joe's girlfriend, Iola, is killed by a bomb meant for Joe and Frank, the two brothers vow to punish her murderer. The killer is still on their trail, but before Joe and Frank can turn the tables on him, they're snatched up by The Network, a secret government agency that desperately wants the Hardys under wraps for their own good.