Free from the author via KDP Select @
Amazon:
Touch the Sky by Robert Elmer, 8th in his Young Underground series of YA historical action adventure thrillers set in occupied Denmark during WWII, this volume originally out from Bethany House in 1997.
A morning flight over Helsingør turns dangerous when the pilot, Matthias Karlsson, blacks out without warning. Almost as terrifying is the find thirteen-year-old Peter Andersen makes in the cockpit—a hidden handgun! When Matthias comes to just in time to save their plane from crashing into the sea, Peter puts the shocking discovery behind him—for the moment.
Certain Matthias is hiding something, Peter persuades Henrik Melchior to join him in spying on the man, and the friends witness a suspicious nighttime meeting with a foreign ship captain. What's worse, a mysterious stranger appears to be spying on Matthias, too.
Suddenly, Peter, Elise, and Henrik find themselves at the center of a dangerous plot. If Matthias is involved, are the Melchiors in danger also? If so, Peter may be about to lose his best friend!