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The Elite Specialist Undercover Squad are asked to provide backup for DS Barbara Hall, who has been undercover for six months and is believed to be acting as a mule for Miguel Morena, a drugs importer who is thought to be negotiating a huge shipment of cocaine into Britain. When Hall fails to make contact of her arrival at London's City Airport, the team become suspicious. Has she gone OTS and joined forces with Moreno, or has she fallen for his associate?

When Hall is murdered, DI Brown is determined to prove that DS Hughes was somehow involved.

When junior secretary Peter Gleeson commits suicide after being exposed as being a homosexual, the team go undercover to investigate a private drinking club called the Golden Goose where they become embroiled in scandal, blackmail and tragedy.

Owner Pauline Monroe's sidelines in drugs and prostitution appear to be the key to unraveling the entire scam, but Hughes and McEwan come close to becoming embroiled themselves. As Edna discovers the truth, tragedy strikes when a drunken Monroe unleashes a gun on DI Brown.

DS Harper comes face-to-face with an old adversary when DC Frankie Li goes undercover as a martial arts expert as the team investigates a corrupt Hong Kong businessman, whose suspicious cargo being brought in a cheese van alerts the team to a much bigger operation involving locating the student catalyst for the Tiananmen Square riots.

As an important identity is finally revealed, and an attempt to rescue his granddaughter backfires, resulting in Harper taking out the prime suspect – as well as two other civilians.