It's the dark days of World War II. America is denying any interest in the conflict, whilst London is being destroyed. And then the enemy make the sort of mistake that many have been praying for: Pearl Harbour. Soon, thousands of US troops are heading across the Atlantic; but what will they find and how will they cope with modern warfare?

The recruits are eager to get into the fighting after training in the USA, but disaster strikes on their arrival when radar is knocked out in a German air raid, leaving the incoming American transport planes unprotected.

Group Captain Barker has no spare squadrons to escort the Americans, especially since the whole of Archie Bunting's squadron is on leave at the wedding of the artistocratic pilot Charlie. Bunting's hungover squadron are recalled early, but only Archie has a plane with him, the rest have to get back by train.

The American airbase to which the transport plane is heading is attacked and bombed by the Luftwaffe, and the furious Colonel Hewitt is forced to go with Barker to the English base.

Meanwhile, Archie contacts base and is given directions by Tully, who forgets to mention the incoming Americans and only warns Archie that there are enemy aircraft in the vicinity. Archie spots a plane and goes into an attack. The American plane believes it is being attacked by the Germans and confusion reigns until Archie realises that he has shot up an American plane. When the Americans spot him in his spitfire they assume he has chased off the Germans.

Hewitt is livid at what he sees as total incompetence and threatens to report everything, although all the Americans on the plane are convinced they were attacked by a horde of Messerschmitts.