The old hidalgo Don Alonso Quijano, maddened by the excessive reading of books on chivalry and determined to become a famous and heroic knight-errant, leaves his village and sets out on the road in search of adventure, accompanied by his faithful friend Sancho Panza.

A doctor invites his relatives to his castle, all the while planning to murder them when they arrive. However, when he himself is murdered, the relatives know they have to find the killer before he gets all of them.