What is the conflict in the book Pretty Little Liars?

The climax to Pretty Little Liars is when the text messages from "a" are interfering with the girls lives. "a" took Hanna's mom's money that her mom stole from a lady in her building and "a" is giving Hanna chances to get her mom's money back. Since Aria is dating her English teacher Mr. Fitz, "A" has been trying to get Aria's mom to catch Aria in the act. Emily has been dating Maya and "A" is a bit jealous so "A" is trying to play tricks on Emily. And lastly we come to Spencer. Spencer's sister Melissa is married to Spencer's Field Hockey coach, Ian. Spencer suspects Ian did something to Alison and "A" has been trying to tell Melissa about what he did last summer.