Banner in the Sky, Paperback/James Ramsey Ullman

The Citadel It stands unconquered, the last great summit of the Alps. Only one man has ever dared to approach the top, and that man died in his pursuit. He was Josef Matt, Rudi Matt's father. At sixteen, Rudi is determined to pay tribute to the man he never knew, and complete the quest that claimed his father's life. And so, taking his father's red shirt as a flag, he heads off to face the earth's most challenging peak. But before Rudi can reach the top, he must pass through the forbidden Fortress, the gaping chasm in the high reaches of teh Citadel where his father met his end. Rudi has followed Josef's footsteps as far as they will take him. Now he must search deep within himself to find the strength for the final ascent to the summit -- to plant his banner in the sky. His father died while trying to climb Switzerland's greatest mountain -- the Citadel -- and young Rudi knows he must make the assault himself.