The Endeavour's attractive new scientist learns a bitter lesson in security when she innocently arranges passage to Townsville for a colleague. Customs officer Morgan and the Minus Five team are held at gunpoint by the passenger who demands the surrender of counterfeit money plates which have been discovered attached to the ship's hull.

A wreck with a cargo of whisky hangs precariously on a ledge on the Reef. A puritan Scotsman plans to destroy the cargo, and a drunken beachcomber warns the Minus Five team, who are working to retrieve a new navigational aid from the wreck. The navigational aid must be assessed, for if it is defective it could endanger the other five ships it has been issued to, but their work is hampered by the old Scotsman who is determined to destroy the whisky before it can cause any evil.

A mad scientist, intent on preserving the Barrier Reef from exploitation, plants explosives aboard the Endeavour as the crew wait to welcome the Royal Britannia during the Royal Visit to Townsville.

A Japanese submarine sunk during World War 2; a Shinto burial service; and the unusual interest displayed by a Member of Parliament plunge the Minus Five team into a new mystery on the Barrier Reef.

A strange illness threatens the life of three people on the Great Barrier Reef when an old scientist loses control of dangerous research into the effects of radiation on the cycle of marine life.

A wealthy fisherman hunts for a world record size shark, and baits an area with bloody meat. One of the Minus Five divers becomes trapped by a thrashing shark pack attracted by the bait.

The owner of an illegal fishing fleet is desperate when the Minus Five team find a strange tripod on the sea bed which is his early warning system. He sends out a bogus distress signal to lure the Endeavour away from the area.

The idea of icebergs in the tropical waters of the Barrier Reef at first amuses the Minus Five team, but the situation becomes grim when the icebergs prove to be real and a threat to shipping. Captain Ted King asks the inventor of the icebergs on board the Endeavour to join the team.

A deadly, radioactive 16½ inch cylinder, released into the sea near the Great Barrier Reef from the crippled spacecraft Apollo 13, must be recovered and contained before the whole area becomes a graveyard. The assignment is given to the Minus Five team.

A bizarre attempted murder by the Mafia can only be prevented by a marine biologist and the Minus Five team working together. They must catch a deadly stone fish alive so that an antidote can then be made to save the dying man.

An ageing sea captain who was the original skipper of the Endeavour determines to scuttle the ship so they can die together. Alone with him on the ship, Tracey Deane tries to change his mind.

One of the Minus Five team acts as bait to catch a company official selling classified information about a newly discovered nickel field on the Barrier Reef.

The Minus Five team find an unconscious diver in the water and another on the sea bed. Attempting a rescue, one of the team gets nitrogen narcosis and tries to give a shark boxing lessons.

When the roof of a cave below the Great Barrier Reef collapses and traps one of the Minus Five divers, the others have to work against time to rescue him.

The Minus Five team clash with big business wanting to exploit a tropical island, even though it would mean the extinction of millions of protected seabirds.

A live missile embedded in the coral reef makes a dangerous proving ground for a celebrated Royal Australian Navy diver who has lost his nerve.

A monster turtle and a blonde diver girl form a strange alliance to frustrate the Minus Five team's latest assignment.

Foreign voices are heard by Kip over the radio as he searches below the Endeavour for one of his tools. The Minus Five team are challenged by strange divers who accuse them of spying.

A desk-type security agent involves the Minus Five team in a dangerous duel with jet-boats when two men are discovered tapping an undersea cable and selling information to a foreign power.

The Minus Five team play cops and robbers with a pearl smuggler, and one of the team becomes trapped in an underwater cave.

The Minus Five team become involved in a lover's quarrel, which quickly turns very serious when the girl involved is trapped in a cage on the sea bed, and all evidence points to attempted murder.

The Minus Five team need all their skill to locate and rescue Kip Young, who has been overcome by the energy force of a sonic fence which was laid to warn submarines approaching the Great Barrier Reef. (Final episode of the series.)