Well, a common plot in Haleb fanfiction is them getting back together after a big break - up. Maybe Hanna is in some sort of trouble and Caleb comes to her rescue, realizing how much he still loves her. Or perhaps they are both trying to start a new business together and face all kinds of challenges that test their relationship.
One idea could be Haleb going on a secret adventure together away from all the drama in Rosewood. They discover a hidden place that has a connection to one of the mysteries in town. Another could be them dealing with family issues together and growing even closer through it.
In some versions, the pregnancy could be a turning point for their relationship. They might become more committed to each other. There could be a plot where they try to keep the pregnancy a secret from 'A' at first because they are afraid of what 'A' might do. As the pregnancy progresses, they could also face financial difficulties and have to figure out how to support the baby while still dealing with their own personal issues and the drama in Rosewood.
Well, a great plot could be that Caleb finds a strange encrypted file on his computer that seems to lead to a hidden treasure in Rosewood. As he tries to decipher it, he has to team up with some unexpected characters from the show. Maybe he also has a vision or a strange dream that leads him to believe there's something supernatural going on in the town related to the file. Also, he could get into a situation where he has to choose between his loyalty to his friends and his own personal gain from the treasure.
Emily could be a great addition. She's their friend and could offer support or get involved in some of their adventures. Spencer is also a good choice as she's always in the middle of the mysteries, and her intelligence could help Haleb in some situations.
One idea could be Aria exploring a new art form in Paris for a semester and getting involved in a mystery there related to the 'A' games. Maybe she meets a mysterious artist who seems to know more about her past than she does.
One idea could be that one of the main characters discovers she's pregnant and has to keep it a secret from the 'A' threats. She might be afraid that 'A' will use the pregnancy against her or her friends.
One idea could be that Paige and Emily go on a road trip together to discover more about their relationship away from the drama of Rosewood. They could encounter various challenges along the way that test their love and loyalty to each other.
Another plot could be Mike developing a relationship with one of the new characters in town. This new relationship could be complicated by the secrets and drama that always seem to surround Rosewood. For example, the new character could be related to one of the 'A' suspects, and Mike has to figure out if he can trust them.
One idea could be exploring a different backstory for one of the main characters. For example, delving deeper into Alison's life before she disappeared. Maybe she had a secret friendship with someone outside of the main group that no one knew about. This could add a whole new layer of mystery to the story.
One idea could be exploring the family secrets of the Liars' parents before they were born. Maybe there was some kind of feud or alliance between the families that the Liars are unaware of. Another could be a story where one of the Liars discovers they have a long - lost relative who has a connection to 'A'. For example, a cousin who has been watching over them all this time.
One idea could be a character getting a drastic haircut as a form of rebellion against the 'A' mystery. For example, Spencer might cut her hair short to show she's taking control of her life instead of being constantly tormented. Another could be a character getting a haircut to disguise themselves from 'A'. Like Hanna changing her look completely with a new haircut to avoid being recognized while trying to figure out who 'A' is.