An unnamed spy—perhaps the same reluctant hero of The IPCRESS File—is sent to Paris to deliver a file of nuclear secrets to a French doctor, but soon finds himself sucked into a twilight world of sex, blackmail and hidden motive, where friend and enemy become indistinguishable. A 'clinic' on Paris's Avenue Foch designed to cater lavishly for multiple perversions, equipped with devices ranging from an Iron Maiden to psychedelic truth-drugs - that's the set-up operated by the enigmatic Monsieur Datt. Naturally, it has a hidden purpose: to compile dossiers of tape and film on influential political clients from East and West. Into this twilight world of decadence and hidden motives come the agents of four world powers. Are they after Datt's pornographic blackmail dossiers? Or is their purpose altogether more deadly than a trip to the blue movies?