One possible plot could be that Cat and Beck are cast in a play together where they have to play romantic interests. As they rehearse their kissing scenes, they start to develop real feelings for each other off - stage. Their friends initially tease them but then start to see how much they truly care for one another.
Well, perhaps there's a situation where Cat and Beck get lost in a strange place during a field trip. They have to rely on each other for survival. In the process, they share some deep conversations and a moment of vulnerability leads to a kiss. After that, they have to figure out how to deal with their new - found feelings in the context of their group of friends.