The Courier is about a British businessman named Greville Wynne (Benedict Cumberbatch) who is enlisted to go undercover to get intelligence on a nuclear missile attack that's being plotted against Cuba. Under the leadership of Emily Donovan (Rachel Brosnahan) and Dickie Franks (Angus Wright), he forms an alliance with Oleg Penkovsky (Merab Ninidze). Together, they try to stop the planned nuclear weapon attacks.