Who is Pips captor in chapter 53? What two mysteries does the captor resolve by admitting involvement?

Pip goes to the marshes to a shack near the limekiln where he is to meet the anonymous writer. There Pip is jumped by Orlick who ties him up and tells him that he is going to promptly kill him. Pip does not want to die, not because he values his own life, but because he still has moral obligations to fulfill with Magwitch (getting him out of the country) and Joe (asking for forgiveness).

Orlick admits to hitting Mrs. Joe over the head, but says it was Pip's fault because Pip was the favored one and Orlick was jealous. Orlick says he is working for Compeyson and assures Pip that Compeyson will make sure that Magwitch does not leave the country.

Just as it appears Orlick is going to kill him, Herbert, Startop and Trabb's boy burst through the door. Orlick escapes.

Pip had dropped the anonymous letter at home and Herbert found it. He and Startop came to the town and got Trabb's boy to show them where the shack was. Pip rests a day at home; the following day they plan to escape with Magwitch.