I think I've had an intruder break into my house (of the feline kind).
Was working in the study, living room window was open at the front with a flat cat & one french door open with velcro'd chicken wire about 3'6" high across it - the normal for mine in this weather. Got a bit stuck in with work & didn't go in the living room for over a couple of hours.
Girlcat was scrabbling at the bottom of the chicken wire looking distressed. When I came in the room she charged to the other end & scrabbled at the Flat Cat screen (she's never done this in 2 years). Then she started dashing up & down under the windows. I shot upstairs to find Boycat (in the wardrobe, phew) & back down. In that short time the chicken wire had been pulled away from the velcro, though luckily Girlcat didn't seem to want to go over there at all.
Re-affixed the chicken wire and closed the door, noticing that the wire had also got a sort of dent in the top. Boycat & Girlcat kept moving round the room sniffing, especially by the french doors & the curtain by that. I then saw their beloved Yeoww banana was pretty wet, and the room had a sort of musty smell to it. Took Girlcat a good couple of hours until she settled down properly.
So I'm pretty sure that the new local tom has somehow got in (possibly OVER the chicken wire), sprayed or peed on their banana, then broke out again when I went up to check on Boycat.