Mr Prentice was an alien living on Earth. For a long time, he fought evil, saving planets, galaxies and universes.
He decided to retire, and enjoyed the seaside in Keelmouth in 1933, so much that he borrowed technology from an advanced civilisation to put Keelmouth in a stasis so it would always be 1933. This affected the residents of Keelmouth, including the residents at Mrs Hutchings' guest house, so that they thought it was 1933.
By the time the First Doctor arrived at the guest house, it was actually 1999. He tried to convince Prentice to put things right, but Prentice tried to argue that this was a perfect time in human history. The Doctor recruited Craig Atkins, of whom Mr Prentice was fond, to pretend to have whooping cough. The Doctor told Prentice that the disease had no cure in 1933 but did in 1999. With the Doctor's help, Prentice turned off his technology. When Prentice asked where he belonged, the Doctor told him that England had plenty of seaside resorts "stuck in the past without the need for any technology." (PROSE: Bide-a-Wee)
In an alternate timeline where Polly Wright was manipulated into interfering with temporal nexus points, Polly told Prentice that Craig was faking. Prentice reacted by sending Susan to 12th century Nottingham. (PROSE: That Time I Nearly Destroyed thet World Whilst Looking for a Dress)