As night fell, the promised storm blew up around them. Spray from the high waves splattered the walls of the hut and a fierce wind rattled the filthy windows. Aunt Petunia found a few moldy blankets in the second room and made up a bed for Dudley on the moth-eaten sofa. She and Uncle Vernon went off to the lumpy bed next door, and Harry was left to find the softest bit of floor he could and to curl up under the thinnest, most ragged blanket. (Harry Potter and the Sorcerer's Stone)
There’s some vagueness in the sentence: (1) ‘left’ seems like a predicative complement for Harry, and ‘was to’ means ‘was obliged to’. (2) to-infinitive clause means the result of ‘was left’ –– Harry was left and he found ~. Which one is right or is there some meaning otherwise?