Chris Lomax has just started working at Chilford Green Aerodrome. Friendship soon develops between Chris and Sarah, a young woman who ferries light aircraft between Chilford and other airfields. Although he is slightly worried by a couple of incidents, Chris's training takes priority, and he is thrilled when head pilot and instructor Jeff Strong takes him for a trial flight - albeit with a terrifying surprise.
Chris has ha his first lesson - learning not to panic! But he has other concerns: cash disappears, and strange noises are heard in the spares store Meanwhile, and Asian man, Bandara Lal, is searching for his missing son - and Chris finds the young boy hiding in the spares store. He tells Chris that he broke into the light refreshments box in search of food. Chris promises to help.
Having found Cham, Chris smuggles food into the store for him, although the boy refuses to give his father's name. Chris eventually finds Cham's father hiding in a ditch. Meanwhile, boss Ritchie has been alerted, emergency sirens sound and vehicles hare across the airfield. When Chris overhears Jeff and Ritchie refer to a 'snooping' intruder, he wonders what sort of trouble he is getting into.
Ritchie calls Chris a 'troublemaker' - and Chris sees yet more clearly that something is amiss. He pays a visit to Putapec, the company for which they are transporting goods, but when he sees the newly landed crate being opened, four cramped, bewildered Asian immigrants emerge. Chris now knows Chilford's secret, and hides in the back of a Putapec van to try and discover more.
Chris, trapped inside a Putapec van, manages to escape when the driver is called away. Back at the airfield, Sarah tells him that Ritchie is on his trail, and Chris finds a badly beaten Cham hiding in his room; he tells Chris how he came to be at the airfield. Chris tells Sarah all he knows, and they discuss ways to try to stop the racket. While Lal tells an all to familiar story of extortion, Jeff is about to leave..
Chris and Sarah, hidden in Jeff's plane, find themselves in Belgium, where Jeff is to pick up more 'cargo'. Determined to expose the racket, they board a Cessna. Sarah is forced to make the most dangerous take-off she has ever attempted as shots are fired; with Jeff in pursuit, they know that their landing back at Chilford will be more hazardous still. Ritchie, meanwhile, learns that Chris has been hiding Cham.
Chris and Sarah land safely at Chilford, and the authorities know about the racket. The means by which Ritchie and his gang have consistently managed to beat Customs is revealed, and a Special branch detective, Farnwworth, searches Ritchie's office and finds his secret cache...