Nathaniel Scrope

 was saved by the Second Doctor and Jamie McCrimmon from being attacked and soon befriended them. The Doctor told John Thurloe about Scrope and it was revealed that he was an undercover agent. At the time, Scrope saved Ben from the marshes and they saw Prince Rupert who Scrope discovered was Prince Rupert. Scrope told Thurloe of this. Thurloe let Polly and the Doctor go to World Turn'd Upside Down to look for traces of conspirators. They met Christopher Whyte there who told them that Oliver Cromwell was to be assassinated while addressing the Rump Parliament. (PDA: The Roundheads)