DP left the door open by mistake and Cookie and Biscuit popped out. It would appear Biscuit just sat on our doorstep and meowed a bit, but poor Cookie freaked out and hid under a neighbour's car. She had to be lured in with gourmet perle.
For the 5 minutes before I found her, I was so terrified. She's not too streetwise and would probably try to befriend moving vehicles.
DP is a little traumatised. Here they are after.