A World War II hero returns to Germany to solve a mystery -- and meet an enemy

Updated 7:27 PM ET, Sat November 10, 2018

(CNN)Clarence Smoyer's index finger caressed the trigger. Sweat poured down the leather flaps of his helmet. No one in his tank moved or even whispered.

It was March 6, 1945, and Smoyer was part of the Allies' last push into Nazi Germany. The lanky 19-year-old with a mop of curly hair was part of a tank crew that had crawled into the German city of Cologne for what would become the US Army's biggest house-to-house fight in Europe. The Germans called it "Endkampf," the final battle for their homeland.
"Gentlemen, I give you Cologne," Smoyer's commander announced over the radio. "Let's knock the hell out of it!"
Smoyer didn't need any added motivation. Before he entered the shattered city, he'd received word that his cousin and his wife's brother had both been killed in the war. Those bastards are going to pay, he vowed.