It's not a random departing protestor that shoulders Desmond- rather, one of the taller of Fagin's boys. The shove is planned, Nancy stepping into Desmond's way just slightly so that he's colliding with her. Nancy plays at getting her balance, and in the process manages to go for Desmond's wallet.

With any luck and quite a lot of skill, she'll be able to slip it back into her pocket without him even knowing.

"No, no, I'm sorry," she says, hands on his rather impressive biceps to steady herself needlessly. "I should have been watching where I was going." Over Desmond's shoulder, her partner in crime disappears. She'll meet up with Georgie later.