Theatre of the Mind ( comic story ) Summary . An elderly - looking man asks spiritualist Diamanda to speak to the deceased Esmerelda . Looking into her crystal ball , Diamanda claims that Esmerelda is happy and requests money for more information . . . only for the man to reveal that Esmerelda is fictional . Taking off his disguise , he reveals himself as Harry Houdini and scolds Diamanda for offering false hope at the expense of people ' s money . The spiritualist confirms his accusation , but adds that after acquiring her crystal she has in fact been hearing dead voices , " and so much more besides . . . " Diamanda orders the crystal ball to save her , and Houdini is met by a milky white vortex . Using his pocket watch to create a signal , Houdini mutters that there is only one hope for him . . . The Twelfth Doctor follows Houdini ' s signal to 1925 . Much to Clara ' s confusion , he claims that the temperature is nonexistent , like " an irrelevance that somebody forgot to add . . . " They see Houdini on stage ; traps of several varieties mysteriously form around Houdini , and the magician does not appear to hear the Doctor ' s calls for him . The Doctor and Clara attempt to reach Houdini , but find a transparent , " intelligent crystal " barrier blocking them . The Doctor shatters the crystal using his sonic screwdriver . Even as they reach Houdini , the Doctor and Clara are unable to hear him . Additionally , the time travellers are attacked by a heavy sand bag which they only narrowly avoid . The Doctor and Clara see the attacker from a distance , and Clara decides to go after her . She follows the mysterious woman offstage , but the woman is gone . Even more shockingly , costumes begin to attack Clara ; however , the Doctor once again uses his screwdriver to save her . The Doctor realises that Houdini is in a computerised system created by the intelligent crystal , and that he is attempting to reprise his greatest escapes in order to get out of the situation . The Doctor attempts to find a way to crash the system , which Clara manages to do by merely whacking the crystal ball with a shoe . Houdini is now free . . . but the woman who attacked the time travellers claims that he will not escape alive . She is Diamanda , but is in the process of being devoured by the crystalline life . Impressed by the Doctor ' s mind , Diamanda hopes to get it . Ropes form around the Doctor , Clara and Houdini , before they are put into traps . Clara is in a water tank , but she manages to tip it over , and Houdini breaks the ropes holding him to a guillotine . The Doctor is apparently in a box falling onto large spikes ; however , he reveals to have never actually been in the box . Clara mentions how she wishes there was an escape key to hit , giving the Doctor an idea . He suggests he , Houdini and Clara think of the thing that makes them feel most free - the TARDIS , an aeroplane and the Doctor himself respectively . This sends the three back to the real world . Houdini wishes he can speak to the dead . The Doctor is unsure as to whether this is possible ; however , he assures Houdini that his reputation will survive long after his death , allowing communication in the form of help and inspiration . Plot . " to be added " Notes . The story has no formal credits . However , the people who worked on the story are seen credited on a playbill for a play within the narrative as a part of the scenery , right beneath the story ' s title . On the playbill , Roger Langridge is given the themed billing of " Master of Ceremonies " , James Offredi is " Lighting " and Scott Gray and John Ainsworth are " Producers " . External links . " to be added "