A bump on the head sends Hank Martin, 1905 auto mechanic, to Arthurian England, 528 A.D., where he is befriended by Sir Sagramore le Desirous and gains power by judicious use of technology. He and Alisande, the King's niece, fall in love at first sight, which draws unwelcome attention from her fiancée Sir Lancelot; but worse trouble befalls when Hank meddles in the kingdom's politics.

In Colombia, mining engineer Rian Mitchell discovers Carrero, the lost emerald mine of the Conquistadors, but has to contend with notorious local bandit El Moro's gang and with coffee planter Catherine Knowland's love.

In this unusually accurate biography, small-time hood Al Capone comes to Chicago at the dawn of Prohibition to be the bodyguard of racketeer Johnny Torrio. Capone's rise in Chicago gangdom is followed through murder, extortion, and political fraud. He becomes head of Chicago's biggest "business," but moves inexorably toward his downfall and ignominious end.

Smith is an iron-willed railroad detective. When his friend Murray is fired from the railroad and begins helping Rebstock wreck trains, Smith must go after him. He also seems to have an interest in Murray's wife (and vice versa).

A fugitive in British Burma hides on a tea plantation, thanks to a mutual attraction with owner Gwen Moore.