As the Mongols invade Baghdad in 1258 the Caliph escapes the city and heads to Basra with his young son, Ali. The Mongols catch the Caliph and he is killed but his son evades capture. In the desert Ali finds the hideout of the only resistance force, the forty thieves, and he joins them and grows up as one of them. Meanwhile his betrothed, the fair daughter of Prince Kasim, is taken to Baghdad by her father to be married to the Mongol leader, Hulago Khan. Ali goes to Baghdad and captures her but soon sets her free. She learns that he is her betrothed as well as the leader of the band of thieves. Her wedding to the Khan is set for Ramadan and so Ali Baba and his band of thieves must attend the celebrations and free the princess and Baghdad.