The hunt for hammerheads continues off Socorro Island, and Dr Pete Klimley hopes to uncover the mysteries of shark migratory behaviour.

The Shark Men are challenged as never before. They hook two giant tiger sharks, but their sheer power catches them off guard.

After a long period of frustration, modified tackle brings the crew success. Two female tiger sharks, Sharon and Lizzie, are added to the tally.

As the long, gruelling mission starts to wind down, the tally of tagged sharks continues to rise – along with tensions between the team.

Expedition leader Chris Fischer pushes the team to the limit as they seek one more tiger shark and three more silvertips before leaving the area.

The team battles shark-finning poachers as they attempt to tag hammerheads in the waters surrounding the Cocos Islands.

When Todd hooks a giant tiger shark and the divers abandon a scientist in dangerous waters, it leads to a growing divide over safety issues.

The team finally adds hammerheads to their list of tagged sharks, but the relentless pace of work is wearing some of the men down.

In the last days of the expedition, the team tries everything from midnight fishing to swimming with sharks to tag the elusive hammerheads.