Task: Question Generation
Input (English):  Almayer s Folly is about a poor businessman who dreams of finding a hidden gold mine and becoming very wealthy. He is a white European, married to a native Malayan; they have one daughter named Nina. He fails to find the goldmine, and comes home saddened. Previously, he had heard that the British were to conquer the Pantai River, and he had built a large, lavish house near where he resided at the time, in order to welcome the invading country to the native land. However, the conquest never took place, and the house remained unfinished. Some passing Dutch seamen had called the house  Almayer s Folly . Now, Almayer continually goes out for long trips, but eventually he stops doing so and stays home with his hopeless daydreams of riches and splendor. His native wife loathes him for this.
One day, a Malayan prince, Dain Maroola, came to see Almayer about trading, and while there he falls in love with Nina. Mrs. Almayer kept arranging meetings for Nina and Dain. She wanted them to marry so her daughter could stay native, because she was highly distrustful of the white men and their ways. Dain left but vowed to return to help Almayer find the gold mine. When he does return, he goes straight to Lakamba, a Malayan rajah, and told him that he found the gold mine and that some Dutchmen had captured his ship. The rajah tells him to kill Almayer before the Dutch arrive because he is not needed to find the gold now. The following morning, an unidentifiable native corpse is found floating in the river, wearing an ankle bracelet very similar to Dain s. Almayer was distraught because Dain was his only chance at finding the secret mine. (The corpse was actually of his slave, who had died when a canoe overturned. Mrs. Almayer suggested that Dain put his anklet and ring on the body.)
Mrs. Almayer planned to smuggle Dain away from the Dutch, so he would not be arrested. She snuck Nina away from her father, who was drinking with the Dutch. When he awoke from his drunken stupor, a native slave girl told him where Nina had run away to, and Almayer tracked her to Dain s hiding place. Nina refused to go back to avoid the slurs of all the white society. During all this arguing, the slave girl had informed the Dutch of Dain s whereabouts. Almayer said that he could never forgive Nina but would help them escape by taking them to the mouth of the river, where a canoe would rescue them from the Dutch. After they had escaped, Almayer erased the lover s footprints, and went back to his house. Mrs. Almayer ran away to the rajah for protection, taking all Dain s dowry with her. All alone, Almayer broke all his furniture in his home office, piled it in the center of the room, and burned it, along with his entire house, to the ground. He spent the rest of his days in  [His] Folly , where he began smoking opium to forget his daughter. He eventually died there.
Output (English): What did Dain vow to come back and help Almayer with?