East End chancer Harry Cole is consumed with a burning desire to transcend his social class and when World War Two breaks out he joins the British army in France and reinvents himself as the suave Captain Mason. He becomes involved with an attractive French nurse, who persuades him to set up and run an escape line. As the debonaire Captain Mason, he helps dozens of soldiers to safety, including one Airey Neave. But when his true identity is discovered by the Secret Intelligence Service (MI6), Harry is faced with his toughest moral dilemma - the acceptance he craves at the cost of betraying his comrades-in-arms. Meanwhile, back in London, Neave is furious that Harry had the gall to impersonate a British officer and sends instructions to apprehend Harry at all costs. Harry realises he is involved with forces far more ruthless and devious than he could ever have imagined...