Two hours later - I should have reminded myself about the word "gradually" - Orbit went out again and decided to wander up the fire escape and onto the wall next to the Tesco carpark where I couldn't reach her.
OMG I was so worried - ran (yes, ran, in my slippers) round to the carpark and fought my way through the bushes to try and grab her, but the little minx looked at me and strolled along the wall in the other direction! So I couldn't do anything else but go back home and wait for her - and she did eventually come back, but I was stressed out the entire time!
Enough outside adventures for today, methinks, she's inside for the rest of the day!