Black satin evening gown with silver brooch found

I found a black satin evening gown this afternoon around 2:15pm, lying over a bench outside Blackwell's on Broad Street, Oxford. It's a Calvin Klein collection piece, size UK 12, in good condition with a delicate silver brooch at the waist and a subtle crystal detailing along the neckline. The gown has a soft but sturdy feel and a navy-blue satin lining peeking from the slit at the back. One unique feature is a small fern-shaped pin attached to the inside of the bodice tag, with a faint perfume scent from last night. I'm hoping to get it back to its owner soon; happy to help return it through the app.