Complex sentence: To conceal his identity Simpson's letters were secretly dropped at a designated place, where a boy was sent to receive and deliver them to the office of "The Aurora" where they would soon appear in print.
Split into simpler sentences: To conceal his identity Simpson's letters were secretly dropped at a designated place, where a boy was sent to receive them. The boy would then deliver the letters to the office of "The Aurora" and would soon appear in print.