What is the falling action and the theme of the short story, "the trombone."

the trombone
jerry stepped off the bus at the music school, and he mentally reviewed the correct trombone slide positions as he walked to room 10 at the end of the hall. he sat down at his chair in front of the music stand and smiled eagerly at nadine, his teacher, who gave him a strange look.
“where’s your trombone? ” she asked.
“oh, no! ” he’d left it on the bus! “what’ll i do? ” he asked, after explaining the situation to nadine.
“you’ll have to get it back, or your parents are out nine hundred dollars.”
“oh, no.” he clapped his hands to his face in despair.
she sent him home without a lesson. the bus ride back was pure agony. it reminded him of the previous bus, where the catastrophe had occurred. fortunately, this driver, to whom jerry confided his plight, advised him to call the bus company’s lost and found. but it was six o’clock; the bus company’s phone recording said that the lost and found closed at five.
the next day, jerry’s father drove him to the bus company office, and—the trombone wasn’t there. no one had turned it in.
“i’m an idiot,” jerry moaned, as his father drove him to the music school to meet his doom. “i never do anything right.”
“you’re not an idiot, you’re a normal kid, and you do a million things right. now you’ll never do this kind of thing again. if the trombone doesn’t show up, we’ll work out a way for you to pay for it over time.”
walking the corridor to room 10 beside his father, jerry felt like a pirate walking the plank. with a feeling of dread he opened the door. inside stood nadine, working the slide on a trombone but not putting the mouthpiece to her lips. wait—the trombone had a familiar dent on the bell and a familiar little scratch on the mouthpiece. it was his!
“someone turned it in at the desk,” nadine smiled. “a passenger from your bus. goodness for honest people, huh? ”
jerry sank into his seat with an immense sigh of relief, and vowed to himself that he would never do anything wrong again in his life.