Vivien Rook

Vivien Rook was a reporter investigating the mysterious "Harold Saxon", for the Sunday Mirror. In 2008, she was called by James Curtis, deputy head of Mildfields School, whom she was friends with, who voiced his concerns about Harold Saxon and his background after a Commemoration Speech he just gave at Mildfields. She looked into it, and called him later to tell him that she didn't find anything, and was greeted by Curtis recalling his concerns and remarking about Saxon's history with the school. Vivien noticed he sounded off in his response, particularly after ending with a remark about forgetting "Harry Saxon." (PROSE: Speech Day)

After doing more research, she turned up at 10 Downing Street claiming to be seeking an interview with Lucy Saxon. She told Lucy the truth about Saxon, explaining that he had only been in existence since Harriet Jones' downfall. However, Saxon had already told Lucy about his true identity and intentions, and Saxon himself came in and ordered four Toclafane to kill Rook.

However, she had a contingency plan and prepared an email message to be sent to Torchwood if she hadn't returned to her desk by 10pm that day. It was retrieved by Jack Harkness, the Tenth Doctor and Martha Jones on Martha's laptop. Vivien had attached the Saxon files, including the Archangel document, which allowed the three to find out how Saxon had mind-controlled most of the world and use it against Saxon. (TV: The Sound of Drums)

Behind the scenes
Russell T Davies would reuse the name Vivien Rook, albeit spelt Vivienne Rook, in his 2019 television series Years and Years. In the show, Rook is portrayed by Emma Thompson.