A kidnapper known as the Scorpion threatens a Senator on the eve of his departure for Puerto Rico, so Joe goes along as his daughter's bodyguard while Frank tries to discover whether the kidnapper's attractive daughter is involved in the plot.

 In London, a group of former secret service agents plan the biggest robbery in Britain's history. Their target is the crown jewels.

The Hardy Boys (Shaun Cassidy, Parker Stevenson) open a third season on a down note: Joe's fiancée is killed in a hit-and-run auto accident shortly before their wedding, setting him on a reckless trail of vengeance. First of two parts.