I really don't know. I've tried to read that story, and the mixture of archaic language (e.g. "I beg you will not...") and typographical errors (e.g. "be" for "he" and "bad" for "had") make it incomprensible. I suspect that the nature of those errors points to OCR software (Optical Character Recognition); this may suggest what original printed words have turned into "thigh", "light", "box" etc. (which make for a very confusing context) - but nothing springs to mind.
The other possibility is that one of the characters is known (from some wider context) to have a bad leg - which would give "spare your thigh" some meaning. Another possibility is that we are dealing with an old meaning of light as a verb meaning "land". The possibilities, given the two huge variables (archaism and possible typos), are endless.
My advice is to buy a book.
Student or Learner