Alex[13] is steering when Elixir sails for Apollo Bay with Granddad Morgan and sister Jess[11], on her first overnighter. As they leave Western Port, Alex and Granddad are surprised when a submarine surfaces nearby, but they sail by unnoticed in their yacht as Jess sleeps below. Once on course in Bass Strait, Granddad radios the sighting to water police, but expects to hear no more. Granddad has the midnight watch. While the children sleep, drug smugglers from the hijacked submarine board, smash the radios and threaten Granddad. They deliberately circle the yacht in their RIB and kick up a huge wake. The boom swings wildly and hits Morgan. The thugs see Morgan slump and speed off. Shocked Alex and Jess recover and make a plan to get safely into Apollo Bay harbour. They assume that as witnesses, they will be killed if caught. The plan works and they escape to the hills, through the town, hunted by the thugs. In the forest, Alex meets Tam[12] and her dog Jill. Alex and Jess come to rely on Tam as a brave friend. She especially likes Alex. Tam’s policeman dad suspects that the young pair are burglars, but Tam defends them. He later realises that there are drugs and criminals involved and that Tam’s new friends are innocent, but in serious danger. Pursuit and betrayal combine to keep Alex and Jess hiding in the hills. Tam helps them and convinces her dad to rescue them. He requests a Federal Police squad to capture the submarine and its deadly cargo. Meanwhile, volunteers from the seaside community rescue the young heroes from their scary but ultimately successful adventure.