1940 finds Adam Southey in a mood of bitter resentment: he cannot join up because he is lame. But at the school where he is teaching, the headmaster, Sam Cooke, is a brilliant scientist. And Adam suddenly finds that the battleground is not the only place to fight a war - for Dr. Cooke has developed a deadly secret weapon and enemy agents are after the plans. Adam and the doctor move to an engineering works in Scotland to build a working model of the weapon. Here, in the wild beauty of the Highlands, Adam is drawn into a desperate game of cat and mouse with the enemy - and he meets Brenda, who is young and beautiful and in terrible danger. . .