Edward Ekubo [David Oyelowo] is a case officer for MI5 who relentlessly watches Waleed Ahmed, a British citizen of Yemeni descent, under the suspicion that he has been radicalised and could be plotting a terrorist attack on the UK. The concerns are not shared by his supervisor and the head of his section, who doubt the solidity of the evidence, leaving Ekubo frustrated as his instincts seem dismissed. He also feels his career prospects are being hampered by systemic bias—being black and having studied at Warwick rather than the more prestigious Oxford or Cambridge—adding a personal layer to the professional tension he faces.
A hidden camera catches Ahmed mentioning a trip to attend the wedding of a cousin in Yemen, but Ekubo’s informants challenge this, pointing to a long-running feud between the cousins that would make such an invitation unlikely. Still, Ekubo persuades his superiors and MI6 that Ahmed is a credible threat, and plans are set in motion for follow-up actions in Yemen. Soon after, Ahmed is arrested by Egyptian police along with several others at a farm where castor oil plants—plants whose seeds can be used to manufacture ricin—are being cultivated.
Ekubo travels to Cairo to continue the case and crosses paths with local MI6 officer Tony Coveney [Stephen Campbell Moore]. The detained men confess to assisting with ricin production, but their statements are withdrawn under pressure, and it becomes clear they have been tortured. The British officers must report Ahmed’s accusations of abuse to the British government, escalating the case. As delays mount, Ekubo asks a colleague to uncover the name of the interrogator from Egypt’s State Security Investigations Service—Colonel Hazem Ashraf [Makram J. Khoury]—who offers to use “persuasive techniques” to retrieve a UK address where Ahmed might have sent ricin. Ekubo also inspects the farm and finds three aerosol cans that the police overlooked, which Coveney arranges to send to London for analysis.
Back in London, further red tape and bureaucratic slowdowns hamper progress. Ekubo questions Ahmed directly; Ahmed proclaims his innocence and says the intercepted emails in which he and a contact mention “linen” are literal references to bedsheets, not coded instructions for ricin. He hints that the ricin is already in the UK and goads Ekubo about his race, provoking a heated moment in which Ekubo physically restrains him. Desperate for a breakthrough, Ekubo calls Colonel Hazem Ashraf for assistance and meets him the next day in a coffeehouse, where the colonel provides an address in Derby. When Ekubo and Coveney return to the police station, Ekubo realizes Hazem’s claims of having used psychological techniques on Ahmed are false—Ahmed’s treatment reveals clear signs of torture. The Derby address proves false as well, though one of the aerosol cans tests positive for ricin.
Returning to London, Ekubo is summoned to the office of the head of Section G. She reveals that the coffeehouse meeting with Hazem was captured by an activist blogger in Egypt who is investigating the colonel, and that the story is about to break publicly. He is suspended with immediate effect, effectively ending his career in the service for the time being. The Ahmed case ultimately leads Ahmed and his lawyer to file a lawsuit against the British government, leaving Ekubo to wonder whether the ricin threat still looms somewhere within the UK.
