The machine is so unpredictable that Donald's nephews warn their uncle that he might end up at any time in the past, and thus advise him to do the testing at the Stonehenge, which has remained unaltered for millennia.
Donald, Gyro, and the boys travel to the United Kingdom to test the time machine at Stonehenge.
There, the ducks meet "King Arthur"—Artorius Riothamus, the last descendant of Lucius Artorius Castus, and find out that he is nowhere near the glorious benevolent ruler history has made him to be; instead, he's a common warlord without much morals to speak of.
Fearing the ducks are Saxon invaders, Arthur has Donald and his nephews imprisoned.
He is just about to execute Donald, but at the last moment, Gyro sounds a car horn, which scares the Britons off.