A Connecticut Yankee in King Arthur's Court is the story of Hank Morgan, a 19th Century mechanic, who after a bump on the head, wakes up inexplicably under an oak tree in medieval Britain, in the year 528AD. 

After being hustled off to King Arthur's Court, he is imprisoned, tried and sentenced to death. Whilst awaiting his impending execution, it dawns upon him that, as crazy as it seems, he is in 6th century Arthurian Britain, and that since he's traveled through time, he is probably the smartest man on the planet right now.