Former best friend suddenly very aggressive

Hello everyone,

I have two cats, Max (a 2 y/o neutered male) and Frankie (a 4 y/o spayed female) and I live in a town house with an enclosed back yard. On sunny days, I like to let them both out into the yard to enjoy catching some rays. Yesterday, I was in the yard with them, just conducting business as usual. All of a sudden, a stray cat appeared on the top edge of our very high solid wood fence. Max is naturally very easily frightened, and ran back in the house, stopping at the glass door to watch. Frankie however decided to challenge this cat and went into full attack mode, though she could not reach the cat or climb the fence. Eventually I successfully shooed her back inside, but then disaster struck. As she went back in the door, she came upon Max and started attacking him in earnest. I wrestled them apart and Max bolted upstairs. I kept them separated for several hours, then tried to let them be together again seeing as everyone had calmed down. No luck however, and she attacked him again. I separated them overnight and ended up putting a baby gate between their two areas this morning. However, Frankie still freaked when curious Max came to sniff the gate, and I had to put her in the bathroom to keep Max out of harm's way.

What can I do? I have no idea what happened. These two have been best friends for two years, they nap together and groom each other. I have no idea what to do and I'm very worried about both my babies I appreciate any advice you can give me!

This is called redirected aggression. Frankie couldn't get at the cat who had invaded her territory so she took it out on poor Max. Here's a recent thread with lots of suggestions on his you can get them back to normal. Many vibes.

http://www.thecatsite.com/t/274482/redirected-cat-aggression-in-my-two-males

Thank you so much for the link! I'm a little confused reading that thread, is there some kind of guide I could follow knowing that redirected aggression is the issue?

There isn't a guide per se, but there are several good suggestions to try. The most important one is introducing them slowly as if they were strangers. It will take time and patience. Here's an article written by Jackson Galaxy that offers an example.

http://www.littlebigcat.com/behavior/redirected-aggression-a-case-study/

You may want to get some 'calming treats' from Amazon to keep around, it might calm him down a little faster. If it makes you feel any better, my two do exactly the same thing! I feel so sorry for the 'innocent' one! Good luck and tell us how you come out!