Ambush is heading for Cairns until a sudden signal puts her on unexplained duty for another six days.
A maor naval exercise involving an aircraft carrier and four patrol boats brings Lt. Keating into open competition with his brother.
Commanding Officer of HMAS Ambush is determined to give no quarter either to Mason, skipper of a cruiser and suspected drug runner, or to Able Seaman Kelly, a troublemaker on board Ambush.
On a very hot day the crew of HMAS Defiance are given permission to swim in the sea ""HANDS TO BATHE"" Sub Lieutenant Rob Matthews is on watch for Sharks. When he goes below to find his sun glasses one of the men in the water is badly injured. Captain David Keating must find out weather the man was accidently shoot becuase of skylarking or he was really attacked by a shark.