On secret orders from Hitler, General ""Willi"" Meirhausser is gearing up for Germany's last-ditch stand, commanding an Alpine defense force headquartered at a mountain war fortress at Aosta; and sharing Meirhausser's bed is beautiful widow Countess Riva Savoldi, the castle's owner. Meanwhile, however, Canadian S.O.E. intelligence officer Captain Ed Kimball is getting information about Meirhansser's plans, hearing rumors that a massive ambush will await the Allies near Brenner Pass, where Meirhausser is readying secret German fortifications. Can Kimball stop Meirhausser from carrying out this scheme? Well, he has one big advantage: Meirhausser's gal Riva is Kimball's ex-lover, and she's now a double-agent for the Allies. So Kimball knows just where to aim his secret mission. With help from speleologist Joelle Gaussin (who knows the cave system under the castle) and US demolitions expert Sgt. Vincent Marco (son of Cosimo, a supportive Italian partisan leader), Kimball parachutes into the hills, blows his way through the caves, and into the castle dungeons. Reunited with Riva, Kimball steals the fortification plans from Meirhausser's safe, then blows up the dungeon behind them as they escape via stolen locomotive:Joelle dies in a fire-fight; Kimball takes a leg wound while fighting German ski patrols; and a wild makeshift toboggan ride gets the surviving members to safety in Switzerland. Implausible throughout, but chockablock with pure action in the Alistair Maclean manner.