Doctor, who uncharacteristically has lost his sense of humour, says “it’s far from being all over” and abruptly departs for the TARDIS. Though weak, the Doctor gathers enough energy to rescue Polly and Ben. He collapses and transforms into a younger man. Production All four episodes of this story feature a specially designed graphics sequence used for the opening titles and closing credits. Designed by Bernard Lodge, they were intended to resemble a computer printout. In the opening credits of the first episode, Kit Pedler is incorrectly identified as "Kitt Pedler". In the opening credits of the third episode, Gerry Davis is incorrectly identified as "Gerry Davies". William Hartnell did not appear in the third episode. On the Monday before the programme was due to be recorded, he sent a telegram to the production team informing them that he was too ill to work. Gerry Davis rewrote the script to explain the Doctor's absence (his sudden collapse) and gave his dialogue to other characters, most noticeably Ben. This was not as much of an interruption to the episode's production as it would seem, as all four episodes had been written so that Hartnell would have relatively little to do in case of just such an event. The original draft of episode 4 did not feature the Doctor regenerating at the end. The First Doctor's last words were originally scripted as something similar to "No... no, I simply will not give in!" Time was running short towards the end of production, and director Derek Martinus opted not to record the line, wanting to ensure that the regeneration sequence was recorded as well as possible. As a result, the First Doctor's last words were simply "Ah! Yes. Thank you. That's good, keep warm." The line cut from the script by Martinus suggested that the Doctor was refusing to give in to the regeneration process. In 2017, Doctor Who writer Steven Moffat exploited this idea and created an extended narrative around the Doctor delaying his regeneration for the episode "Twice Upon a Time". The episode uses original footage from The Tenth Planet alongside new scenes with David Bradley replacing William Hartnell, in which the First Doctor meets his future self, the Twelfth Doctor, played by Peter Capaldi. Cast notes During the regeneration sequence at the end of the final episode, Patrick Troughton momentarily makes an appearance – uncredited – as the Second Doctor.