Surprisingly, he finds he will leave Dover richer than he arrived. He'd watched a man doing the three-card trick, and when he learned it he set up for himself. Because he's a boy, people stop to have a go. It's their loss. He adds up what he's got and what he's spent. Deduct a small sum for a brief grapple with a lady of the night. Not the sort of thing you could do in Putney, Wimbledon or Mortlake. Not without the Williams family getting to know, and talking about you in Welsh.
(Wolf Hall by Hilary Mantel)
What does "a brief grapple with a lady of the night" mean? It sounds like buying sex.