Here's a plot idea! I don't know if you'll be ok with the worldbuilding, but we could tweak it.

In the night, a mysterious cat visits Curlstar. It's dark and she can't see his face. She was just woken up and assumes she's dreaming. She's also very tired and not paying attention. The cat has her make some kind of contract on Starclan that she doesn't read (I know they wouldn't have a contract, I mean something verbal/spiritual that binds her). The agreement is that she will destroy (the colonies/ rainclan/ other colonies except for rainclan). She wakes up in the morning and laughs at the weird dream. cut to regular life. A few nights later, when she's awake before she goes to bed, the visitor returns and asks why she hasn't started fulfilling her promise yet?

The visitor could be Falconpaw or Snakepool, someone from another clan, someone from the dark forest, or some wanderer like Sol with a random vendetta.