After Smith coldly sacrificed Lee Thomas to distract the Germans, his fellow Nazi spies Olaf Christiansen and Ted Berkeley become desperate to escape from their situation before either Smith decides they're disposable, too, or, worse yet, they're actually taken back to England to be executed for treason.
A word of critique. Although the way in which Smith uses Thomas as a decoy shows some keen improvisation on his part, there really isn't any reason for him to insist on bringing the three traitors along. Since they have nothing to look forward to back in England is a firing squad, they're less likely to cooperate... especially now that they've seen Smith ruthlessly dispose of one of them.
As a consequence, what occurs when the group makes their way to the castle's cable car station is entirely Smith's fault.
Needless to say, desperate men do desperate things, and as soon as they see an opening, Christiansen and Berkeley attack their captors and steal the cable car, leaving Smith, Schaffer, Mary and Jones stranded in the station with loads of German soldiers beating on the doors.
Likely because he realizes this is his fault, Smith rushes after them and jumps on the roof of the cable car. Figuring two against one is good odds, Christiansen and Berkeley open the doors and climb up top to fight him. Christiansen tries to shove him off. Smith, armed with a pick, swings it at Christiansen, who dodges. Berkeley isn't as lucky, and the pick slices through his arm. Badly wounded, he abandons the fight and climbs back down inside the car.
More tussling follows. Christiansen slips, and tries to save himself by grabbing Smith's legs. Smith prevents the other man's weight from dragging him down by jamming his pick into the roof and holding on.
The death scene that follows is a little disturbing to watch. Sure, Christiansen is a Nazi spy and a traitorous scumbag, but watching him whine, beg and plead as he slowly slips while Smith looks on impassively is pretty pitiful. As is Berkeley's weak attempt to help his friend by trying to reach through the window grab his belt with his one good arm.
Ultimately, though, with a terrified scream, Christiansen slips and falls down, down, down towards the German woodlands thousands of feet below.