Read it through once

“My dear, there is an upper window in the prison, to which Charles can sometimes gain access at three in the afternoon. When he can get to it--which depends on many uncertainties and incidents--he might see you in the street, he thinks, if you stood in a certain place that I can show you. But you will not be able to see him, my poor child, and even if you could, it would be unsafe for you to make a sign of recognition.”