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?