The Doctor wakes up in a strange place. He seems to be in a cell. He finds a device constructed out of spare parts and a bunch of library books in the cell. He speaks out loud and notices his voice sounds funny. He starts to rub his chin and realises he has a beard. He uses a shiny book cover as a mirror, and sees that he is in the Master's body. The Master has realised his escape plan won't work. He knows he will be back in his cell soon. He thinks about leaving a trap in the Doctor's laboratory, but decides not leaving one will confound the Doctor.