Moffat initially doubted Gina Bellman's suitability for the role of Claire Jackman because he associated her too much with Jane Christie, the character she had played in his sitcom "Coupling". Moffat did not imagine the character to be as beautiful as Bellman, but her audition was so good that he revised his vision of the character. Bellman originally auditioned for the role of Katherine, but the producers wanted someone younger to play that role. However, Bellman said that she talked herself out of the role by arguing that there should be an age gap between Katherine and Claire to avoid Katherine becoming a threat to the wife. Bellman approached her role as if Claire had become caught up in Tom's mid-life crisis, an angle that impressed the producers.