Two young English women go on a cycling tour of the French countryside. When one of them goes missing, the other begins to search for her. But who can she trust?

Led by Kim Philby, Plan Aurora is a plan that breaches the top-secret Fourth Protocol and turns the fears that shaped it into a living nightmare. A crack Soviet agent, placed under cover in a quiet English country town, begins to assemble a nuclear bomb, whilst an MI5 agent attempts to prevent its detonation.