A great plot idea might be Noel Kahn starting his own detective agency in Rosewood. He could be investigating strange happenings around town that the Liars aren't even aware of yet. This would give him a chance to be the hero and use his wits in a different way. Also, a plot where Noel has to face his family secrets coming to light and how he deals with that while still maintaining his cool exterior in front of his peers would be really interesting.
To develop Noel Kahn's character further, you could explore his family background more deeply. Maybe he has a troubled family history that has made him the way he is. For example, if he has an overbearing father, it could explain his sometimes - over - confident behavior. Another way is to put him in more moral dilemmas. For instance, having to choose between loyalty to a friend and doing the right thing in a difficult situation.
One idea could be that Aria and Noel team up to solve a mystery in Rosewood that the other Liars are unaware of. They might discover a hidden connection between their families that has been kept secret for years.
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.
Perhaps a plot where Mona and Noel start a secret relationship and have to keep it hidden from the rest of the liars. They face challenges like jealousy from other characters and the fear of being found out, which adds a lot of drama to the story.
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 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.
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.
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 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.
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.