14th-century Franciscan monk William of Baskerville and his young novice arrive at a conference to find that several monks have been murdered under mysterious circumstances. To solve the crimes, William must rise up against the Church's authority and fight the shadowy conspiracy of monastery monks using only his intelligence – which is considerable.

Caesar has had enough when another legion is hacked to pieces by the damned single indomitable village in Gaul because of the druid's magic potion, so he decides to tackle the problem at the root before conspiratorial senators exploit his humiliation: sycophant Lucullus is ordered to capture the druid (believed immortal) and push him over the edge of the earth (according to the story still believed to be flat as a pizza; actually Greeks and Romans knew better). By pure luck, Lucullus' first net traps both druid and Obelix's pet dog, so the giant and Asterix follow them by ship on the Atlantic, and crash after a storm on the North America coast in pursuit of the druid who was catapulted off the Roman galley before Lucullus triumphantly sets sails back for Europe. They find the druid and meet a tribe of Indians (believing to be in India), literally a whole New World for the equally primitive Celts. At the home front, Caesar sees his chance to overrun the village, but has to wait till the last magic potion has run out, hoping the heroes won't return. In America, the medicine man has a bad eye in the foreigners, especially when the druid proves a dangerous rival...

Inhabitants of the last unconquered village in Gaul (ancient France) use a magical potion to hold their independence from Roman invaders.

An intellectually nonconformist friar investigates a series of mysterious deaths in an isolated abbey.