Plots Involving Other Clans

Here I have a list of plots that involve more then one Clan

Involving 4 Clans
2 clans fall out and have a war, and one of the other two clans has a water shortage and goes to the remaining clan for help.

Involving 2 Clans
You could have the leader mate with another cat from another Clan, then he/she keeps it a secret from the rest of the Clan. But then the mate from another Clan (if you want to add drama, it can be a medicine cat) gets found out by his/her Clanmates, and they threaten to banish him/her if the two lovers don't reveal themselves.

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An idea for a plot involving breaking the warrior code would be to have two cats from different Clans mate and have kits. Both parents want to raise their kits, and the pair of mates end up arguing over their kits and turn into enemies. Their fight could eventually lead their Clans into battle. If you want to add more drama, you can even make one or both cats medicine cats, leaders, or deputies (because generally speaking those cats are the most important cats in the Clan and shouldn't break the warrior code).

Involving Any Ammount of Clans
Okay, so the story starts out in a morning through an apprentice's point of view. It's the day of the Gathering. This is the apprentice's third Gathering, but it's still exciting to them. They fidget while they're training and hunting all day. Finally the Gathering comes. The warriors go to the Gathering place, and it begins. Then, right as a leader is announcing a new warrior, a loud yowl is heard. The cats hurry over to the source of the noise and see a dead, bloody warrior laying on the ground. The murderer is nowhere in sight. From here, it's one giant mystery the apprentice solves. It can just be a mystery, or you can add the twist that there a cat that is falsely accused.