An escaped prisoner, Matt Kirk, and his accomplices hijack an ambulance in Sydney, taking hostages at Fort Denison (Pinchgut) to escape detection while heading north. A siege situation ensues as police, led by Superintendent Hanna, try to negotiate a peaceful surrender, but tensions rise after one of the men is shot and injured. The situation becomes increasingly desperate as the group's true intentions come into focus: Matt demands a retrial for his wrongful conviction in exchange for not firing a gun that could cause significant damage at a nearby munitions ship, leading to a tragic confrontation.