It's 1940, and the world is at war. Linus, a swift, has always dreamed of flying with the Royal Bird Force and making a name for himself as a squadron leader. So when he and his sister, Ava, have the opportunity to volunteer, he jumps at the chance. But it's a dangerous journey, and Ava goes missing before they manage to reach the airfield for training. Now, Linus has two missions: help the war effort and find his sister. Linus will face bomber planes, arrogant falcons, and a spy who's determined to take him down. He is brave and fast and kind - but can Linus prove that helping win the war is more about the size of your heart than the size of your wings?