Woke at 4am this morning to the sound of cats fighting and soon realised it was inside the house. Quickly realised that our cat was in and on my bed, so she was not involved. She looked terrified and ran to the attic! I am pretty sure she had not been involved at all as she seldom goes out at night and she seemed like she had woken when I did.
It was such an eerie sound - one cat sounded like it was being terrorised by the other and the victim almost sounded human, like it was crying mummy. I even went and checked on ds 
. It definitely sounded like one cat was intimidating the other. Trust it to happen when dh was away - I was too scared to go and look at first, but when I did put the stair light on they both scarpered.
Is this normal - to enter another cat's house and fight there? Could there be some connection to our cat? Like teaching her a lesson? Probably being hysterical here. I have had a cat flap for 15 years (basic model) and nothing like this has ever happened before - I don't even recall having benign visitors, but our previous cat was a bit of a bruiser and our new girl pretty timid, while there are two very dominant cats over the road - I bet one of them was involved.
I suppose there is nothing I can do other than invest in one of those super-expensive cat-flaps.