The Octopus - S4.E13

The spies have a vital mission - they must protect a ship carrying the last component required to make a nuclear bomb. Other ships carrying nuclear parts have been raided by pirates and MI9 have intelligence to suggest that this ship will be targeted.

The team use Frank's mini-submarine to follow the ship, in an undercover, underwater mission. Meanwhile, Frank is very worried about the team since his cousin Charlton went missing in the same waters some years back and was never found.