The woman from the beggining is rather conservative in her veiws on gender and sexuality, in the raving lunatic sense. We're talking explosive anal retention. She's also sporting a hefty sense of psychopathic narcissism.
She's not seen her sister in a few years, so naturally there's a sense of inexplicable connection, and of physical similarity to her - feeds into the narcissism and intrigue as to why this new and most alluringman knows her, but is being rather mysterious. She's blind to the truth, doesn't want to connect the two deep down.
The sister wishes to reconnect to her family and roots, yet also knows it's never going to work what with the large dose of crazy. Like if you travel back in time to meet a friend who dies in the future.
The sister can't take the lies, and decides to meet one evening, to set things straight. The slightly awkward, yet totally earnest approach is misinterpreted. The woman sees this as a chance to bed such an attractive, intriguing man.
It leads to a clueless/horror movie style finish.