Em and Liz are sent to therapy by their step-parents because of the special bond the two share. Though not directly related, the stepsiblings are so close to the point of feeling what the other one feels. Doctor Clarke is fascinated by the case and wants to write about it, so he conducts a particular experiment with them to observe: he starts stimulating one of the girls to see if the other one reacts. As the exercise progresses successfully, the therapist tries turning things up a notch and having sex with them, realizing that Em and Liz's bond is an absolute case study that needs further research.