The Hardy boys spot peculiar, alien-like people on an old missile site being guarded by federal agents.

Joe Hardy is still haunted by memories of his dead fiancee, but has to focus his mind on the case when Jocco's girlfriend overhears him talking to the police on the phone. Meanwhile, Frank Hardy tries to help Joe by going undercover too, but Jocco finds out and traps Frank in a shark-infested area.

Joe and Frank Hardy go to London to find their missing father, but when Frank goes missing as well, Joe and an agent from the British Ministry must find a traitor together.