Sentence:  “The story of this <WSD>adoption</WSD> is, of course, the pivot round which all the circumstances of the mysterious tragedy revolved. Mrs. Yule had an only son, namely, William, to whom she was passionately attached&thinsp;; but, like many a fond mother, she had the desire of mapping out that son's future entirely according to her own ideas. [...]" 
Meaning of the word marked with <WSD> tags:  The state of being adopted; the acceptance of a child of other parents as if he or she were one's own child.