Under the diligent eyes of agent Jean, Palmer's intuition edges them closer to the professor while gun-for-hire former MI6 man Randall is always one step ahead. A tip-off from a key witness draws Jean and Palmer closer to the truth.

Their hunt for the scientist takes Harry and Jean to Beirut, where they close in on Randall - but the line between personal and professional soon begins to blur.

Suspecting an American's hand in the abduction of Dawson, Dalby sends Harry and Jean to a Pacific atoll where the neutron bomb is to be tested.

While Jean unravels the meaning of IPCRESS, Harry's incarceration in a brutal American gaol is only the start of his nightmare journey.

Harry Palmer runs from the brainwashing but he cannot hide for long from the agents of Cathcart's conspiracy. Jean discovers the origin of Maddox's conflicted feelings towards his country and Dalby learns that his beloved organization is to be axed.