This is probably one of the best shot I took in London, I think it was probably worth the whole trip up there.
I was in a pub with my fiance, in Richmond, and it was raining non stop. After a - surprisingly good - espresso I spotted a weird guy reading a book in the back of the pub, facing me, close the backdoor. By the time I took my camera to capture him, he moved away. In the same moment another guy show up behind the window of the backdoor, gives a quick glance and... I shot!
He stood still for a second or two, then he walked away.
Talking about being in the right place at the right moment ;)