A new family turns out to be moving next to Jess's house who has a girl named Leslie, turns out that that Leslie is in the same class as Jess.
Jess thinks Leslie is unusual at first because she r aces with the boys instead of staying on the girls side of the black top. But after Jess saves Leslie from Janice Avery on the bus, then they make something in the woods and name it Terabithia
When it starts to rain the creek gets filled with water. So Jess is scared to go to Terabithia because he can't swim and he's scared. But one night Leslie went to Terabithia but dies when the rope breaks.
Jess doesn't know how to handle his best friend's death. At her funeral he felt everyone only cried for them self. But he also realized Leslie helped him change in many ways.
Since the rope broke he maid a bridge of lumber from Leslie's backyard. Once he finishes he surprises May Belle and makes her queen of Terabithia.
I think the theme is friendship. Because Jess becomes Best friends with Leslie but Leslie dies. So Jess builds a bridge to Terabithia in memory of Leslie.