Opaque is a biological weapon which is created by the brilliant and beautiful Helen. One night she steals the prototype sample, while her boyfriend steals a helicopter. Together they head for an oil rig in the North Sea. Vengeance is on Helen's mind and she is driven to reach the rig. When the helicopter crashes Helen uses deception and murder to ensure she reaches her goal. At the rig she discovers a terrible truth as death awaits her. Then the deadly Opaque is accidentally released and a yellow toxic cloud slowly engulfs the rig. Even a squad of SAS soldiers sent to contain the situation cannot stop Opaque carrying out Helen's vengeance on almost everyone it touches.