In his biography of Charles Sumner, David Donald relates how Sumner went to London and got introduced around to everybody who was anybody back in 1837-8 with considerable success. He accepted an invitation to call on "the meretricious Countess of Blessington" who kept a "famous and scandalous ménage at Gore House." Donald says that Sumner didn't think much of her friends Disraeli or Bulwer, but otherwise leaves the subject of what went on there unmentioned.
The reader is supposed to know all about Blessington, I guess; the only reference is to some of Sumner's letters. What's the scandal?
The lady in question is Marguerite Gardiner, nee Farmer, nee Powers, Countess of Blessington. Wiki says she married the 1st Earl of Blessington, Charles John Gardiner, in 1818, about four months after her previous husband's death.Reading between the lines in her biographies suggests Marguerite began her relationship with the earl while her previous husband was still alive.
The "famous and scandalous ménage at Gore House" probably refers to the Countess's relationship with Alfred d'Orsay, with whom she had a very public friendship during the 1820s and 1830s. During part of their relationship, d'Orsay was married to one of the count's daughters by a previous marriage.(!)
Skimming the wiki, she seems like quite a lively character.