a history only you and I

'I'm told it's customary to dance with your wife at these sort of things, not your illicit lover.''What about the abandoned wife dancing with strange women,' Joan returned, a little too tipsy from the wine to fear the repercussions of her forwardness. 'Is that customary?'AU loosely based on the biopic 'The Duchess' (or if you haven't seen it: AU where they're both aristocratic ladies but Joan Watson is the Duchess of Northumberland and unhappily married to a horrible, unfaithful man.)