Tweed - once top Yard detective, now SIS Deputy Director - reluctantly agrees to check out suspect Michael, urged by his old friend, Superintendent Buchanan. Found by Buchanan seated on steps in Whitehall, Michael uttered only three words. 'I witnessed murder.' One by one four brutally ravaged skeletons are discovered. Two of them on Dartmoor, near the mansion of Drago Volkanian, Armenian founder of a giant supermarket chain and an armaments plant. With Paula Grey, his assistant, Tweed relentlessly pursues the unknown killer. Among others, he interrogates the strange Volkanian clan: Lucinda, Drago's stepdaughter, steely and moody; her elder brother Larry, the company managing director. Again he meets Michael, the younger brother, who is still unable to speak. He is suffering from amnesia - or so say two psychiatrists. Unlike Buchanan, Tweed insists the horrific murders are not random. A link must exist between the four victims. He also suspects a foreign power is involved. The tempo ratchets up ferociously. With Paula, Bob Newman and his team, Tweed travels to Marseilles, where murder is a way of life. A desperate battle takes place on a mysterious island. Escaping the city alive by a hairsbreadth, they race back home. Later they return to Dartmoor. Who is the fiendish killer?