When sharks come streaking to the scene a diver is in great peril. 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 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.