The plot concerns the feisty eponymous heroine Isabella. She has been sailing in the Mediterranean, accompanied by an elderly admirer Taddeo, in search of her lover Lindoro. After her ship is wrecked Mustafa, the Bey of Algiers, believes her the ideal replacement for his neglected wife who he intends to marry off to a captured slave, who happens to be Lindoro. Complicated situations ensue involving Taddeo being awarded the honour of Kaimakan and Mustafa in turn becoming a Pappataci, a spoof award invented by Isabella to keep him obeying her strict instructions. All ends well in a rousing finale with the Italians escaping from the clutches of the Bey.