The Prime Minister has been assassinated. Paula Grey rescues a key American from a brutal attempt on his life. Is a giant power determined to absorb Britain into its own system? Enemies flood into the country.

The noose tightens.

What is the role of enigmatic Sharon Mandeville, glamorous millionairess?

Grim Ed Osborne flies in from Washington - with the villainous Jake Ronstadt and his troop of henchmen. Newman sees an informant killed by a mysterious marksman, The Phantom. Tweed moves his key personnel to a secret hideaway. Jefferson Morgenstern, Secretary of State, arrives in London. Tweed meets ladykiller Basil Windermere, playboy Rupert, son of Sir Guy, who made a fortune in the States. Denise Chatel, attractive assistant to Mandeville, appears, disappears. Who is running this gigantic operation? Terror grips London.

Attempts are made to kidnap Tweed, to kill Paula. The trail leads Tweed and his team to Basle, Switzerland, on into the sinister Black Forest.

The murderous Umbrella Men, encountered in London, reappear.

A battle takes place amid the ice-bound forest. Tweed moves on to Strasbourg, then Paris, hunted by The Phantom, identity yet unknown.

The spectacular climax takes place on Romney Marsh as a hostile naval task force approaches Britain.