Tense 1950 s Cold War thriller superbly directed by Anthony Asquith. Behind the net , the wire fencing surrounding the top secret British research establishment Port Amberly, researchers have produced a new weapon that could change the balance of power of the Cold War. Led by Professor Heathley (James Donald) an experimental supersonic jet aircraft code named M7 has been developed. All that remains is to test fly the prototype, and whilst Heathley wants to undertake testing himself his wife (Phyliis Calvert) and his boss believe it is too dangerous. The risks are increased by the presence of foreign agents who are trying to sabotage Heathley s work. Will they succeed or will Britain and her allies gain a crucial advantage in the Cold War?