Could you please tell me the precise meaning of "to be into no mieschief whatever" in the following excerpt from the last chapter of The Great Gatsby?
She showed a surprising amount of character about it too—looked at the coroner with determined eyes under that corrected brow of hers and swore that her sister had never seen Gatsby, that her sister was completely happy with her husband, that her sister had been into no mischief whatever.
This reflection comes from Nick. It is based upon the mournful circus that surrounded the aftermath of Gatsby's death. One such element was Catherine's testimony about her sister, Myrtle. Earlier in the text, it was clear that Catherine knew that her sister was Tom's mistress and that Tom had told things to Myrtle that would essentially "string her along." Yet, in chapter 9, when confronted with the possibility that people would link Myrtle in something scandalous such as an affair with a married man, Catherine lies to defend her sister's reputation. It is here in which the excerpt takes place. Catherine was very convincing with her "determined eyes" as she swore that Myrtle had never seen Gatsby and that her marriage with Wilson was a strong one. Catherine wants to convey the perfect image of her sister. This includes suggesting that she did not stray from her marriage because she was an inherently good soul.
It is here in which the the statement that "her sister had been into no mischief whatever" is used. The idea of "mischief" relates to extramarital activity, socially discouraging behavior, or acting in a manner that would bring tarnish to one's reputation. Essentially, Catherine is suggesting that her sister acted in a way she did not. She is trying to "whitewash" and sanitize Myrtle's memory. Nick does not attribute this to anything more than people taking sides away from Gatsby and using lies and deceit to do so. Catherine does this in suggesting that her "sister had been into no mischief whatever," a statement we know is a lie because, like so many, Myrtle had done everything and anything that could be seen as mischief.