Explain why Magwitch has been moved to rooms where Herbert's fiancée lives. What preparations do Pip and Herbert make for Magwitch's escape?

Back in London, Wemmick tells Pip things he has learned from the prisoners at Newgate. Pip is being watched, he says, and may be in some danger. As well, Compeyson has made his presence known in London. Wemmick has already warned Herbert as well. Heeding the warning, Herbert has hidden Magwitch in his fiancé Clara's house. Wemmick sends Pip a note indicating that now may be a good time to escape with Magwitch and get him out of the country.

Herbert and Pip plan to take the boat out with Magwitch in a few days, take him down the Thames until they run into a steamer headed for a foreign port.