ESUS is an experimental unit set up to try and forge closer links between MI5 and the police force. The unit is headed by MI5 agents, but the rest of the team have been seconded from regional police forces because of their Specialist undercover expertise. ESUS brief is to investigate cases that go beyond the rimit of either the regional police forces or special branch after ESUS. Small-time crook Brian Ha Sung has suddenly acquired a fortune and the team are sent to find out what he's up to. Reknowned for smuggling illegal immigrants out of China the team at first suspect he maybe into drugs. When they go undercover to investigate they discover something very different - an ex double agent from the Soviet Union, who fearing for the safety of his granddaugter, has traded with Ha Sung in return for information on Kim Su Li, one of the leaders of the Tiannamen Square uprising. A kidnapping ensues resulting in a bloody and violent showdown.