Just as the British launch a peace process meant to stabilize its relations with Iran, MI-5 learn that a rogue Iranian intelligence officer, Megan Asnik , may be plotting an attack. Zaf and Adam go undercover in Tehran with the intent to assassinate Aznik before he can cause any real damage. Their attempt to get him fails but results in the death of many innocent Iranian civilians. When Aznik shows up in the British Embassy requesting asylum, he claims to be a double agent who has been feeding the West information about Iran's biological weapons development. His handler is code-named Copenhagen. Realizing they've been set-up, MI-5 needs to identify Copenhagen and find out exactly what is going on.