Ryan and Burke are soon recaptured after escaping from jail ... but by whom?

Buchan is chasing the stolen gold but Nero is one step ahead.

Buchan goes to Paris with the Achilles club while the trio fly into danger.

Ryan and Burke are recaptured but get help from their cell mate.

While the boys go sailing, Sue and Colin track down Nero.

Colin has been shot and Sue is up to her neck in trouble, while Professor Nero is getting closer to perfecting Medusa.

Nero is becoming increasingly insane, Buchan and his team must prevent him from destroying the world.

Ryan and Burke's have escaped with Nero's black box, and they have the boys captive on their yacht. But Buchan is more concerned with the missing gold.

Buchan believes that the coded message found in the box will lead them to Caine and the gold.

Buchan and Caine are racing against each other to break the cypher.

Caine snatches the gold from under the noses of the Dutch police. Buchan follows him to Amsterdam while Sue and Mike take part in a yacht race.

Buchan has car problems, Sue and Mike take to bicycles. Caine has a plan to throw them off the scent.

Buchan has been duped. The teenagers must find out how Caine plans to move the stolen gold.